mesa: Add python to parse the formats CSV file

mesa: Add python to parse the formats CSV file

The basic concept for the format parser was taken from the format CSV
parser in gallium/auxilliary/util.  However, this one has been altered in a
number of ways:

 * Removed big endian vs. little endian stuff (mesa doesn't need it)
 * Better documentation: Almost every method has a full docstring
 * An actual Swizzle class with methods for composition and inverses
 * Over-all cleaner (in my opinion) implementation and class interactions
 * A few bug fixes

Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Brian Paul <brianp@vmware.com>