Added `builder.py` module, removed unnecessary parts of manual
Initiali coding for builder
Builders for simple parser and modes parser are working
Fixed some bugs in builder, did some refactoring etc.
`clap.builder.Parser()` functionality moved to `clap.builder.Builder()`,
some debugging, reference implementation of built interface,
updated manual
Nested mode-parsers can be created using JSON,
major refactoring in `clap/builder.py`, update to version 0.7.4
Bugfixes and stylefixes in `clap/builder.py`