Command line macro definition patch

Found this recipe: http://stackoverflow.com/a/10791845
should now work for gcc as well. Here is the output on window:
In [1]: import xxhash

In [2]: xxhash.VERSION
Out[2]: '0.1.0'

In [3]: xxhash.XXHASH_VERSION
Out[3]: 'r35'
Merge pull request #3 from sfgagnon/master

Visual C Compiler compatibility
Change classifiers
Format adjust
Bump to 0.1.1
Merge remote-tracking branch 'upstream/master' into hashlib-compatibility