v0.12

Update version number to 0.12.

Changes to the C library:

• Fix for some integer printf formats outputting an extra \0.
• Some GCC builtins added to allow linking some maths functions.
• Maths functions added to replace stubs in BBC BASIC.
  • cos, cosf, sin, sinf, tan, tanf
  • fabs, fabsf, floor, floorf, floorl, trunc, truncf, truncl
  • scalbn