Fix MinGW build problem
Use non-recursive Makefiles if possible
Update .gitignore for non-recursive Makefiles
Enable GObject Introspection support

Most GObject things work, but some non-GObject things need API change to work.
Remove unused CFLAGS and LIBS. Allow using libarchive without a pc file.

Unused CFLAGS and LIBS may cause strange error in some system. FreeBSD system
libarchive does not have a pc file installed. Use AC_SEARCH_LIBS to find it,
so FreeBSD users do not have to install libarchive from ports.
Move GTK+ widgets to a separate library

GTK+ support is optional now, but building API documentation requires GTK+
support to be enabled.
Update .gitignore
Enable C99 or C11 support
Remove unused virtual function tables
Remove old and unused variables from Makefile.am
Make all internal functions private

All internal functions in autoar-common is moved to autoar-private, and
their documentation are not generated now. Public functions and data types
in autoar-common are moved to autoar-misc.
Fix typo in autoar-gtk.h include guard
Fix race condition when building GnomeAutoarGtk-0.1.gir
AutoarExtract: Prevent unneeded floating operations

Fractions are not always needed, so I removed change it the same as
AutoarCreate to the prevent unneeded calculation and function calls.
Update doap file to include programming language
Do not add libarchive to Requires when libarchive.pc is not available