Generally we want to avoid accidental change of value of a constant or of a variable. Originally I'd copy value on access, but this changed it so a const Value is returned instead and copy is done only when it's needed.

The function returns string representation of a variable of given Value type, using provided variable name.

Functions operate on it now instead of on just SentenceContext. It's open to additions in future. Main purpose atm is to hold Variables as well as SentenceContext.
Done some cleanup in code too. Updated tests to reflect the FunExecContext change as well.

Claryfing comment for linux antlr lib (it should only be included for final execs not for intermediate libs)

Change StrSet::is_subset_of to correctly handle empty sets, add some comments
Add Tset::insert_symbol
Add tests for new functions
Bump required corpus2 version to 0.1.2 due to a fixed bug there

Implemented command line test for testing values expression.

Do not link antlr lib on linux. Need to investigate error and why does it look like working without the linkage. It's still needed for win tho.

Making the default for "value-if-false" parameter to be a static, initialized on demand, member of Conditional.

Conditional operators realised as if..then..else expression and operator "? val ? pred" with some tests for StrSet specialization

Adding specialization of Equals for positions, as they logically need to take into account actual sentence context for full comparison.

Conflicts:
	libwccl/CMakeLists.txt

Fixing expected interface of sets i.e. bool intersects function, not a function returning actual intersection