Addresses issue #934.
Tested and working on unix and pyboard.
Also use less stack space when printing single precision float. Addition of asinf and acosf addresses issue #851.
Top-level lib directory is for standard C libraries that we want to provide our own versions of (for efficiency and stand-alone reasons). It currently has libm in it for math functions. Also add atanf and atan2f, which addresses issue #837.
