YAMP 1.2.3 (First)

Bugfix for M+M, M-M operations.
Merge branch 'master' of https://github.com/FlorianRappl/YAMP
YAMP 1.2.3 (Second)

Re-added ParseContext.IO.cs, improved function keyword and added ability
to load functions that are defined in files.
Updated portable project to 1.2.3 second