v0.82plus check in, Boundary check, EEprom delta settings, symbolic axis names

1) Checks print envelope boundaries to avoid damaging hardware
2) symbolic axis and named constants ([Xaxis] vs [0]
3) EEprom settings for Delta radius & limit
4) Extruder auto tune additions using cohen-coon method to derive
constants from step response. Always terminates and yields useful
result. Heaters too fast would cancel on overheat, too slow time out.
5) Fixes m117 command to work as documented
6) Fixes %ab format internal document, fixes it when appearing in ram
variables, adds some new fields to monitor, such as line number and
gcode line
7) adds error detection and report for out of bounds positions
8) Adds error detection and report for invalid gcode
9) adds error report 4th page to top level lcd pages
10) fixes code paths that would fail to reset inactivity timeout
11) recognizes lower case gcode letters, optimizes gcode scanning
12) adds implicit gcode line numbers for error reporting, when N code is
missing
13) fixes some missing bounds checks such as extruder index, etc from
gcode
14) adds consistency and limit check functions for eeprom settings. New
items may be added and will always be within safe bounds.
15) Uses symbolic names for printer configuration eg
#if DRIVE_SYSTEM==DeltaDrive not
#if DRIVE_SYSTEM==3
16) fixed some bugs related to inconsistent conditional compiler checks.
17) reversed buffer free from v0.83 by factoring code simpler
18) fixed limit on filenames in SD
19) Increased folder depth allowed in SD