interp/remap: improve support for remapping builtin codes

The G_REMAPPABLE and M_REMAPPABLE macros were getting a bit baroque.
Replace these macros by a bitset lookups, add init code for same.
interp/remap: make G28/G28.1/G30/G30.1 remappable
interp/remap: add G28/G28.1/G30/G30.1 example to remap/getting-started
configs : Add PocketNC configuration
PocketNC configuartion files provided by Duane Bishop <duane@pocketnc.com>

Signed-off-by: Charles Steinkuehler <charles@steinkuehler.net>
Merge pull request #176 from cdsteinkuehler/config-PocketNC

configs : Add PocketNC configuration
rtapi_shmem: retrieve the size of an attached segment.

This was likely an oversight and is needed for introspection, boundary checks,
and a useful Python API to RTAPI shared memory segments.

Fixes #178 .
halmodule: enable attach to existing rtapi shm segment
config -> velocity extruding: wire oneshot.0.width with analog output

added net to analog output so the width of the oneshot can be
easily adjusted with M68 from G-code. Cleaneup of obsolete code in
comments
config -> relocate configuration for velocity extruding

this gives the opportunity to keep the directory clean and
make a README file for explaining how this solution works
Merge pull request #180 from luminize/vel-control-extruding

config -> update and relocating of config files for velocity extruding
config -> add scripts for postprocessing slic3r g-code files
config -> corrected moved config files

due to a move of config files to a subdir the deleted files
were not committed in the 'old' location.
Merge pull request #179 from mhaberler/rtapi-shmem-size-param

RTAPI: retrieve the size when attaching a shared memory segment

After a discussion with Michael, this API change looks mostly internal.  While it could be used externally in a comp, it looks unlikely, and even more so at this early stage of Machinekit's existence.  Therefore, we're not going to worry much about the 'Evolution of Public Contracts' section of C4 [1].

Merging patch.

[1] http://rfc.zeromq.org/spec:22#toc8
config : add pressure adjustment to .hal file

with the lincurve function you can in/decrease extra velocity for the
buildup of pressure in the nozzle. This prevents blobs (release of
the builtup pressure) at the low velocity points

add gcode testfile which you can use for tweaking machine specific settings
config : break up very long lines
Merge pull request #182 from luminize/vel-control-extruding

config : add pressure adjustment functionality on top of other changes
script : fix of bug in postprocess script w.r.t. recharging

When the post processing script finds a retract anchor, it replaces
that with the M commands for retracting. Meaning setting the time
of the retract (time = 0 means 0 seconds retract disconnecting of
the extrudion with the motion). in some cases the anchor for that
in the slic3r generated code is off, resulting in the time being set
after the retract (so no retract) and a precharge then gives too much
script : add fix for timing of setting of retract time in layer
script : remove test comment
Merge pull request #184 from luminize/vel-control-extruding

script : fixes for setting of retracting time when disconnecting extruder from motion