Remove generated files.
Pass the foreign option to AM_INIT_AUTOMAKE.

This allows the dropping of empty files that only exist to satisfy the
GNU conventions.
autotools: Remove unnecessary library test.
autotools: Remove test for PathIsRelative function.
autotools: Remove unnecessary program checks.

All of these tests are either already required by asking for automake or
the programs are not even used.
autotools: Use C++ mode.

Also, remove tests that are C-specific.
Update gitignore.
autotools: Enable silent build rules.
Add sassc++ to autotools files.
Correct small mistakes in the default Makefile.

* A C++ project should use CXX and CXXFLAGS.
* Rules that build actual files should always use the filename as the
  target name.
* Mark some targets as phony.
* Add an all target as default. It's the target name most people use
  since it's the GNU convention.
* Use pattern rules instead of the old style.
Merge pull request #144 from QuLogic/autotools-cleanup

Ooh, thanks for doing this! I'm not so good with autotools and makefiles, so this is greatly appreciated!