Cleanup grammars

Move trivial methods in built-in grammar definitions to the Grammar class.
Reconsider expression position setting in the whole grammar rules.
Make ',' (comma) character reserved, not to use in ordinal identifier token.
Add reader state inspection

Add reader state (Reader.State class) to inspect the progress and internal
states of the reader.
Modify the constructor overloads of ParseException class.
Add reader context handlings

Modify the rules in built-in grammars to handle reader the context stack.
Add transiting expression rules for the pattern grammar.
Fix the transiting expression rule to the standard grammar in the alternative
grammar (re-implement as an extended term).
Improve error outputs of YacqRepl to use information from the reader context.
Merge branch 'feature/reader-improve' into develop
Update packages

Update NuGet library packages.