CFG Recovery and Simplified Interface

This is a major update, that brings:

1. Recursive descent disassembler
2. High-level simple to use interface to BAP
3. New utility `bap-objdump`
4. Enhanced pretty-printing
5. Lots of small fixes and new handy functions
6. Automatically generated documentation.

There're some breaking changes also, like:

1. `Bitvector` is no longer `Identifiable` (i.e., doesn't implement `Identifiable` interface)
2. `Memory.size` is renamed to `Memory.length`
3. Basic disassembler as well as its `Insn` is moved to `Disasm_expert` namespace