Ignore unversioned files
Deprecate Lua 5.0 style modules; Do not register a global table anymore

Use only the Lua 5.1 style for modules, without exporting a global "gd"
table. Avoids namespace pollution and gives transparent support for
Lua 5.2, at cost of the support for Lua 5.0.
Use package.cpath ot detect instalation path

Lua 5.2 pkg-config file do not gives a "INSTALL_CMOD" variable anymore,
so we extract them from package.cpath now. Adds a dependency on Lua
binary for building.
Update version number
Random fixes in the Makefile
Move rules to create the distribution tarball to the Makefile
Put current version number in the Makefile

Avoid repeating the version number at cost of a more complicated build
procedure.
Force "make dist" to fail if the output directory already exists
Remove distribution tarball and temporary directory on "make clean"