doc: Misc. cleanup

Add missing parentheses and whatnot, move dangling comment, etc. Some
specific items worth mentioning:

Fixed some references to non-existent tags, found via `make html`

msgpack_rpc/channel.c:
  ELOG already prefixes each line with "error @ ..."

runtime/autoload/spellfile.vim

@@ -197,7 +197,7 @@ endfunc
 
 function! spellfile#WritableSpellDir()
   if has("unix")
-    " For Unix always use the $HOME/.vim directory
+    " For Unix always use the $HOME/.nvim directory
     return $HOME . "/.nvim/spell"
   endif
   for dir in split(&rtp, ',')

runtime/doc/job_control.txt

@@ -83,7 +83,7 @@ Here's what is happening:
 - The second shell is started with the -c argument, causing it to execute a
   command then exit. In this case, the command is a for loop that will print 0
   through 9 then exit.
-- The |JobHandler()| function is called by the `JobActivity` autocommand (notice
+- The `JobHandler()` function is called by the `JobActivity` autocommand (notice
   how the shell* pattern matches the names `shell1` and `shell2` passed to
   |jobstart()|), and it takes care of displaying stdout/stderr received from
   the shells.

runtime/doc/msgpack_rpc.txt

@@ -74,6 +74,7 @@ There are four ways to open msgpack-rpc streams to nvim:
 
 2. Through the stdin/stdout of a program spawned by the |rpcstart()| function.
 
+							*$NVIM_LISTEN_ADDRESS*
 3. Through the socket automatically created with each instance. To find out
    the socket location (which is random by default) from a running nvim
    instance, one can inspect the |$NVIM_LISTEN_ADDRESS| environment variable:

runtime/doc/nvim_provider.txt

@@ -9,7 +9,7 @@ Nvim provider infrastructure			       *nvim-provider*
 First of all, this document is meant to be read by developers interested in
 contributing to the refactoring effort. If you are a normal user or plugin
 developer looking to learn about Nvim |msgpack-rpc| infrastructure for
-implementing plugins in other programming languages, see |external-plugin|.
+implementing plugins in other programming languages, see |remote-plugin|.
 For instructions on how to enable Python plugins, see |nvim-python|. For
 clipboard, see |nvim-clipboard|.
 

runtime/doc/options.txt

@@ -5522,7 +5522,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 						$HOME/.vim/after"
 					Macintosh: "$VIM:vimfiles,
 						$VIMRUNTIME,
-						$VIM:vimfiles:after"
+						$VIM:vimfiles:after")
 			global
 			{not in Vi}
 	This is a list of directories which will be searched for runtime

runtime/doc/starting.txt

@@ -57,7 +57,7 @@ filename	One or more file names.  The first one will be the current
 		that needs to be saved.  Except when in readonly mode, then
 		the buffer is not marked modified.  Example: >
 			ls | nvim -R -
-		Starting in Ex mode: >
+<		Starting in Ex mode: >
 			nvim -e -
 			nvim -E
 <		Start editing in silent mode.  See |-s-ex|.
@@ -212,7 +212,7 @@ argument.
 		{not in Vi}
 
 							*-g*
--g		Start Vim in GUI mode.  See |gui|. For the opposite see |-v|.
+-g		Start Vim in GUI mode.  See |gui|.
 		{not in Vi}
 
 							*-e*

runtime/doc/term.txt

@@ -25,8 +25,7 @@ NOTE: Most of this is not used when running the |GUI|.
 1. Startup						*startup-terminal*
 
 When Vim is started a default terminal type is assumed.  for MS-DOS this is
-the pc terminal, for Unix an ansi terminal.  A few other terminal types are
+the pc terminal, for Unix an ansi terminal.
-always available, see below |builtin-terms|.
 
 You can give the terminal name with the '-T' Vim argument.  If it is not given
 Vim will try to get the name from the TERM environment variable.

src/nvim/eval.c

@@ -345,13 +345,6 @@ typedef enum {
   VAR_FLAVOUR_VIMINFO           /* all uppercase */
 } var_flavour_T;
 
-/*
- * Array to hold the value of v: variables.
- * The value is in a dictitem, so that it can also be used in the v: scope.
- * The reason to use this table anyway is for very quick access to the
- * variables with the VV_ defines.
- */
-
 /* values for vv_flags: */
 #define VV_COMPAT       1       /* compatible, also used without "v:" */
 #define VV_RO           2       /* read-only */
@@ -359,6 +352,10 @@ typedef enum {
 
 #define VV_NAME(s, t)   s, {{t, 0, {0}}, 0, {0}}, {0}
 
+// Array to hold the value of v: variables.
+// The value is in a dictitem, so that it can also be used in the v: scope.
+// The reason to use this table anyway is for very quick access to the
+// variables with the VV_ defines.
 static struct vimvar {
   char        *vv_name;         /* name of variable, without v: */
   dictitem_T vv_di;             /* value and name for key */

src/nvim/main.c

@@ -1961,7 +1961,7 @@ static void mainerr(int n, const char *str)
 }
 
 
-/// Prints help message and exits; used for 'nvim -h' & 'nvim --help'
+/// Prints help message for "nvim -h" or "nvim --help" and exits.
 static void usage(void)
 {
   signal_stop();              // kill us with CTRL-C here, if you like

src/nvim/msgpack_rpc/channel.c

@@ -723,7 +723,7 @@ static void complete_call(msgpack_object *obj, Channel *channel)
 
 static void call_set_error(Channel *channel, char *msg)
 {
-  ELOG("Msgpack-RPC error: %s", msg);
+  ELOG("msgpack-rpc: %s", msg);
   for (size_t i = 0; i < kv_size(channel->call_stack); i++) {
     ChannelCallFrame *frame = kv_A(channel->call_stack, i);
     frame->returned = true;