It is more intuitive that way, e.g. equal(2,3) is never true, equal(3,3) is always true.
Nowhere is only equal to Nowhere, and Begin or End are equal to nonspecial positions
depending on current position in the sentence context.

* reset_values function to set all Values to their defaul-construct state
* read-only access to all variables of some type via get_all<T>
* Variables cloning
* convenience functions: get_or_throw, get_value
Value subtypes now contain a value_type typedef and require a const value_type& get_value() const member function.

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.

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

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

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

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

Adding some methods to values for use by operators, e.g. equals and is_subset_of/intersection. Some are just stubs.

Add PositionRef value class, add Position:: nowhere/begin/end, add SentenceContext get_[abs|rel]_position takint Position or Positionref
Add tests for sc's get_*_position