Some other refactoring too, some augmented comments etc.

This is to accomodate rules in future, and repurpose "Operator" to be a library api-level class for users of the library, for parsed functional operators.

It's a change from if x then y else z, which wasn't exactly proper anyway without parentheses.

So tools like valgrind don't get too excited that there's still reachable but not freed memory.

My relative position tests wouldn't compile in GCC where I used Position::Nowhere for comparison. Apparently according to standard TC1, section 9.4.2, paragraph 4, if you want to use integral static const in a program, you still have to define it even if there's initializer in the declaration.

RelativePosition operator, represented by "+" in WCCL (at least initially). Returns Nowhere for Nowhere, or a Position shifted by given offset to the position given (Begin and End are first translated into normal Positions).

The Equals<T> now uses helper class EqualityComparer<T> and distinction is in the helper class specialisation.

Checks wether Position is_inside, is_outside, or equals to other Position given the SentenceContext.

It's the "setvar($V, blabla)" operator that sets $V to blabla and always returns True.

Somewhat nicer to use and guards against static init order fiasco.

It is used wherever in WCCL variable is seen in read-only context, i.e. outside of operators that are setting its value like setvar.

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.