Templates can now be reused across projects. The output files are still
put in the root of the output tree because that is where the client
programs will look for them.
There is a convention that one can do `pkg-config --variable=includedir`
and have it return the path to the source files (even if that should
have been taken care of by options in --cflags).
Note that using pkg-config is NOT recommended because of:
1. It doesn't know which language you are using, so language-specific
options such as -std=c++11 or -std=c99 cannot be passed along. Yet,
the build will corrupt if you don't get these correct.
2. It has no means of communicating which defines that should be set
in config.h, effectively disabling them all, possibly leading to
inconsistencies between the library and the executable.
A boilerplate .pc file is provided in the lib/pkgconfig directory. Using
this location has the advantage of being in the same path relative to
the libraries as it will be in the installation. The drawback is that the
lib/ directory no longer contains just output unless one uses out-of-tree
builds.
In the root directory of the project a local .pc file is provided which
instead of the usual end-installation directory rather points to the
build and source directories. By adding the build directory to the
PKG_CONFIG_PATH environment variable, a local build can be referred to
from other projects (such as examples or specific test-cases).
Having two different files is unfortunately necessary since pkgconfig
does not support prefix rewriting on Linux, and having them in two
different directories is necessary since the AutoMake-generated files
is not capable of renaming a file, only relocating it.
