-Fixed bug that caused SDL2/SDL2_mixer to be required even with enable-sound turned off (or SDL2/SDL2_mixer unavailable)
-Updated README with info on libglm and libglew
-Forgot to update English version of readme with libglfw,libglew
-Fixed VMD file-loading bug that caused some VMD files not to load properly.
-Changes made to use with older versions of OpenGL (as low as 3.2)
-Raised min. requirement to OpenGL 3.3
Remove and ignore files generated by autotools.

Leaving auto-generated files sometimes cause problems with newer
changes.

In released packages (tarballs) these file is necessary for users to
build without autotools. We don't develop softwares in the directory
that is extracted from a tarball so the problems won't happen.

However, we, developers living in the Linux world, already have
installed autotools, and the working tree from a repository is the place
where we develop softwares.

We might have to expand the installation instructions but I just
appended the `autoreconf -i` line for now.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
-Lowered to OpenGL 3.3 (going to merge with master branch)
Merge branch 'ignore-autogenerated-files' of https://github.com/omasanori/MikuMikuPenguin into omasanori-ignore-autogenerated-files
Ignore more files gerenated during builds.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>