Modify the type of HolKernel.syntax_fns and add some documentation.

This is in response to issue #247.

The change to the type makes things a little more natural when using partial applications - for example, HolKernel.syntax_fns1 can be used to provide syntax support for regular unary operations.

Add assembly code parsing/printing support for the M0 and ARMv7 models.

There are new entry points to the decompiler. These take a function that maps a quotation (containing machine or assembly code) into a list of strings (typically hex). This facilitate the input of ARM assembly code. For example, the functions:

m0_decompLib.m0_decompile_code
m0_core_decompLib.m0_core_decompile_code
arm_decompLib.arm_decompile_code
arm_core_decompLib.arm_core_decompile_code

are provided with type

: string -> string quotation -> Thm.thm * Thm.thm

The ARM-M0 model is now hooked up to the "core/fast" decompiler.

Various updates/improvements to the decompiler tools.

Reorganisation and improvements for the "fast" decompiler.

Now tentatively called the "core" decompiler.