2010.05 - Openscad — ContextQMD

Added functions and statements
- Added abs() function
- Added exp(x), log(b, x), log(x) and ln(x) functions
- Added minkowski() statement for 3d minkowski sums
Added 'include <filename>' and 'use <filename>' statements
- Old implicit '<filename>' include statement is now obsolete
Some bugs fixed, maybe some new bugs added