WIP:  Initial commit of rtapi_global bindings and master daemon

Cython extension for `rtapi/rtapi_global.h`:
- C extension has enough functionality  to initialize global data
- A Python subclass puts it all together to init global data
- Nosetests

`rtapi_masterd` with pluggable configuration, environment and shm
sanity checks, global data init code, daemonizing code; about half way there?

Other misc stuff:
- Fixes/additions to imported C code from config.h, rtapi/ring.h
- Add function to ring.h to zero buffer
- add 'hal_stack_size' config item and give others defaults
- machinekit.rtapi.compat module:  deprecated; for kmodules
- Start of documentation
- Minor fixes
Remove `machinekit.compat` stuff, replaced by `config`

These became a configuration source in `machinekit.rtapi.config`
Refactor RTAPI_Master_Daemon.txt document
nosetests FixtureTestCase:  add `filesdir` path attribute

Convenient way to get the `nosetests/files` path in a test
fixup:  remove mistakenly committed src/rtapi/rtapi_common.c

Cython generated file
debian/control.in:  add new python deps

`python-mock`:  unit test harness
`python-signalfd`:  for masterd `signalfd` service
`pithon-keas-pbstate`:  for subclassing protobuf classes (this may go away)
machinekit.rtapi.plugin:  ugly way to get plugin by name
new config items:  rlimits
fixes to machinekit.rtapi.{rtapi_global,shm} and cython bindings

Finishes rtapi_global support?
Pull RTAPIcommand into a class and add to nosetests
hal/cython/Submakefile:  move compat_bindings.so to machinekit.rtapi

... from machinekit.compat
rtapi/rtapi_masterd:  fill out skeleton

This is probably mostly obsoleted by the session model refactorings
WIP:  initial commit of masterd
machinekit/rtapi/__init__.py:  collect things for easy import
nosetests/test_120_utils.py:  initial commit
initial commit of src/machinetalk/proto/proto/rtapi_masterd.proto
initial commit of rtapi/rtapi_common bindings
Initial commit of flavor detection

A lot of this is probably in config now, and the rest probably should
be
remove SetuidHelper from machinekit.rtapi Python class
Cython bindings for rtapi_heap

Build Cython bindings for rtapi_heap.

Modifications to rtapi_heap to enable:
- Build rules in `rtapi/Submakefile`
- Struct type fixes in `rtapi_heap.h` and `rtapi_heap_private.h`
- Move `errno.h` bindings into `cython_helpers.pxd`
- Add freelist iterater routines to `rtapi_heap.c`

Also added unit tests