Eliminate Visual Studio 2013 compiler warnings in "pxfmt.cpp".

Some of the templatized functions will only be called for certain format-type
combinations (e.g. from_int_d24_unorm_s8_uint() will only be used with certain
data types).  The parser will create errors for cases that will never happen
(e.g. trying to copy a "double" into a "uint32").  Because of this, certain
type-casts are used in places where you might think that no cast should be
needed (i.e. where a function is only intended to be called in certain cases).
However, casts are used to avoid compiler warnings.

There's also one place where the compiler warned about a "potential divide by
0", but where (as used) this can't occur.  In this case, a compile-time "if"
statement is used to prevent the compiler from generating a warning.  The
optimizer should eliminate the "if" statement, since it will be static for that
instantiation of the templatized function.
Add license section.
Update README.md
Add glxspheres license comment.
Clean up punctuation.
Fix dependencies for pthread dll to always attempt to copy the right dll to the correct location.
Merge pull request #63 from vMcJohn/windows_build_cleanup

Fix dependencies for pthread dll target
Merge pull request #62 from IanAtLunarG/pxfmt_140512_FixWarnings

Eliminate Visual Studio 2013 compiler warnings in "pxfmt.cpp".
Apitrace license cleanup. Closes bug #61.