[doc] fix #7562 by making --helpFull combine --help + old --advanced for easier grepping in a single cmd; add --deprecatedCommands

[timotheecour]

@andreaferretti
shows as:

./bin/nim_temp --advanced

Nim Compiler Version 0.18.1 [MacOSX: amd64]
Copyright (c) 2006-2018 by Andreas Rumpf
::

    nim command [options] [projectfile] [arguments]

Command:
  compile, c                compile project with default code generator (C)
  doc                       generate the documentation for inputfile

Arguments:
  arguments are passed to the program being run (if --run option is selected)
Options:
  -p, --path:PATH           add path to search paths
  -d, --define:SYMBOL(:VAL)
                            define a conditional symbol
                            (Optionally: Define the value for that symbol)
  -u, --undef:SYMBOL        undefine a conditional symbol

...

  -r, --run                 run the compiled program with given arguments
  --advanced                show advanced command line switches
  -h, --help                show this help

Note, single letter options that take an argument require a colon. E.g. -p:PATH.
Advanced commands:
  compileToC, cc          compile project with C code generator
  compileToCpp, cpp       compile project to C++ code
  compileToOC, objc       compile project to Objective C code
  js                      compile project to Javascript

...

  --verbosity:0|1|2|3       set Nim's verbosity level (1 is default)
  --experimental            enable experimental language features
  -v, --version             show detailed version information

NOTE: if needed I could move Note, single letter options that take an argument require a colon. E.g. -p:PATH. outside of ../doc/basicopt.txt to move it to the end of both --help and --advanced

[Araq]

This is a good idea, but we should also change from --advanced to --fullhelp (don't document --advanced, but keep supporting it).

[timotheecour]

/cc @Araq PTAL

[Araq]

Sorry, I did it my way instead.