Fix TokenParser::resetImpl not calling superclass's method
Change DiagnosticMessage constructor parameter

Passing by const reference to Position enforces copy construction of a
shared pointer to SourceBuffer in the DiagnosticMessage constructor. It
is not very efficient if the referred-to Position is a temporary object.
By passing by value, the position sub-object is move-constructed.
Add DiagnosticEnvironment and DiagnosticTestEnvironment classes
Add SimpleCommandParser class
Merge pull request #48 from magicant/feature/simplecommandparser

Implementation of new simple command parser