* added preliminary and partial C11 (and general language) lexing, parsing and AST generation support:
   * the plan is to replace TCC and thus OpenCL C and CUDA preprocessing, parsing and conversion with this in the future
   * additionally this should allow to create generic EBNF/LL(inf) parsers directly in C++
   * lexer: currently it is possible to lex a subset of C11 (major missing features: preprocesser tokens, unicode literals, most integral literals and prefixes/suffixes)
   * parser / AST generation: again, this only supports a subset of C11 right now and furthermore will only validate the input (according to this subset) and _not_ construct an AST
   * grammar: this is a mostly generic solution that should be able to support other languages later on (this creates an LL(inf) parser; heavily inspired by boost.spirit, but obviously much more minimalistic)
   * lang_context: basically the driver class that starts/handles the lexing, parsing and AST generation (and error handling); note that this supports multiple translation units
   * source_types: misc types and enums that are required during lexing, parsing and AST generation