Add strtod(), wcstod(), wcstol() and friends.

This implementation of strtod() replaces the old as it implements
support for parsing hex constants which is needed by various tests.
Add gamma functions.
Make lgamma and friends work, add test.

We can't use weak aliases on variables in emscripten, so get rid of __signgam
and just use signgam.
Another test for negative zero and hex floats.
Add lots of math functions.
Move scalbn to libc to fix broken functionality. Disable test on x86.
Bump version.