GLSL codegen: Improve printing of floats

- use fewer digits after the decimal point for integral numbers
- use more digits to fractional number to ensure correct round trip
  conversions (binary->decimal->binary)
- add a few tests for this
Fixed typo: opengl -> opencl
Merge pull request #523 from white-pony/opencl-check-typo

Fixed typo: opengl -> opencl
Merge branch 'master' into glsl_select_vectorize

Conflicts:
	src/CodeGen_OpenGL_Dev.cpp
Fix comment
Windows build fixes
Merge pull request #506 from halide/generator

Add Generator class and support code
Merge branch 'master' into ucon-generator