extend GCODE_MACROS with a report and eeprom saving options.

[ellensp]

Description

While playing with GCODE_MACROS I noticed there was no way to see the currently set macros. So I added a
optional GCODE_MACROS_REPORT which adds macro reporting to M503 settings display.

eg

M810 Hello world
M812 Testing123
M814 Marlin rocks!
M503
...
echo:; GCODE Macros:
echo:  M810 Hello world
echo:  M811 <empty>
echo:  M812 Testing123
echo:  M813 <empty>
echo:  M814 Marlin rocks!
ok

While I was there I added a second option GCODE_MACROS_EEPROM so the macros are saved and loaded from eeprom if you enable it

Requirements

GCODE_MACROS
Optionally GCODE_MACROS_REPORT
Optionally EEPROM_SETTINGS with GCODE_MACROS_IN_EEPROM

Benefits

Improvements to GCODE_MACROS

Related Issues

Was helping out with https://reprap.org/forum/read.php?415,897251,897252

[thinkyhead]

The reason that this feature never had saving to EEPROM is that we considered it a bad idea to separate the invocation of "anonymous" macros from the G-code that defines them. Macros are meant to be used as shorthand to make the G-code a little bit smaller when something is done repeatedly and frequently. As such they are also meant to be defined in the G-code file so that there is no mixup when inevitably macros get moved around or deleted.

There are better concepts for defining reusable macros in G-code, specifically by having named macros, where it is more clear what the macro is meant to do when invoked, and it is more obvious what code is likely missing when a macro gets lost. It may also be easier to remember a name than the number of some macro defined in the past.

[ellensp]

Its optional. Surely it should be up to the user how they want to use it.