Tune the makefile according to new principles, which adds a few bells
and whistles and for clarity.
Synopsis:
* The dependency on opm-common is completely gone. This is reflected in
travis and appveyor as well. No non-kitware cmake modules are used.
* Directories are flattened, quite a bit - source code is located in the
lib/ directory if it belongs to opm-parser, and external/ if third
party.
* The sibling build feature is implemented through cmake's
export(PACKAGE) rather than implicitly looking through source files.
* Targets explicitly set required public and private include
directories, compile options and definitions, which cmake will handle
and propagate
* opm-parser-config.cmake for downstream users is now provided.
* Dependencies are set up using targets. In the future, when cmake 3.x+
can be used, these should be either targets from newer Find modules,
or interface libraries.
* Fewer system specific assumptions are coded in, instead we assume
cmake or users set up system specific details.
* All module wide configuration and looking up libraries is handled in
the root makefile - all sub directories only set up libraries and
compile options for the module in question.
* Targets are defined and links handled transitively because cmake now
is told about them. ${module_LIBRARIES} variables are gone.
This is largely guided by the principles outlined in
https://rix0r.nl/blog/2015/08/13/cmake-guide/
Most source files are just moved - if they have some content change then
it's nothing more than include fixes or similar in order to make them
compile.
Using an external cJSON installed under /usr/include was not possible before
as the cJSON headers within opm were still used due to relative paths.
With this commit move the copied cJSON source to external/cjson and
thus prevent them to be found if an externally installed cJSON is there.
