Exposes last read character as property in lexer.
Fixes bug in Lexer.Emit.
Renames bootstrap.kasm to test.kasm
Removes LexRules.cs. We have no need for it.
All rules are embedded directly in the Lexer class.
Applies test output of generated tokens in AST parser.
Fixes test program path to test.kasm.
Implements lexer for grammar defined in LANGUAGE.md
Adds LANGUAGE.md. This holds the grammar definition of
the assembly language used to write Kerbatron programs.