- removed uncached input stream adapter; it was too slow anyway
- implemented a class binary_read which parses CBOR based on input
adapters
- in the CBOR parser, numbers are created via memcpy to avoid undefined
behavior

The implementation is non-standard. Deprecation allows a simpler API in
the future without removing any features.

This commit removed the re2c lexer and replaced it by a manual version.
Its integration is not yet complete: number parsing does not respect
locales or overflows. Furthermore, parsing does not need to end with
EOF. Therefore, a lot of test cases fail. The idea is to push this
branch forward so we can conduct performance comparisons. So far, a
nice side effect are better diagnosis messages in case of parse errors.

Instead of overwriting src/json.hpp with an empty file

With GCC 7, there are even more diagnostic flags.

The constructor basic_json(std::istream&, const parser_callback_t) has
been deprecated since version 2.0.0. This commit removes it together
with its code example, deprecation macro, and test cases. The code now
also compiles with -W-deprecated-declarations.

Conflicts:
	.travis.yml
	Makefile