Expression Editor UI Library

Changes since v1:

Apache License
Expression Editor UI library
SeContext: optional variable context to support specific search paths
New builtin function getVar(string varName, vector defaultValue)
return varName if variable exists, otherwise return defaultValue
Fixed compile and usage problems on Mac OS X
Use cmath instead of math.h
Safety checks on exponentiation and power
Updates to documentation / doxygen cleanup
Added pre-generated flex/bison files for use with Windows 7.
remap() takes 5 doubles, not 4 doubles and an int.
Fixed artifacts with voronoi function, when jitter is high
Added mutex to parser

(Internal orignal SeExpr v2.9)