improvements to hint:processing: show import stack, distinguish nims, show includes etc

[timotheecour]

hint:processing is very useful during debugging; this PR improves it further:

• show a (nims) prefix for files processing during nimscript processing to avoid confusion
• show includes as well
• show the importing module (or (toplevel)) and the import stack depth (with >); this makes it easy to trace how we got to process a given file by simply lookup up the import stack
• verboseProcess (which showed a hintProcessing for each top-level statement) wasn't working since a while ago; after this PR it now works again; and you can show those without verbosity:3 (which is very verbose), instead you can use a new hint:processingstmt

example snippet

Hint: (nims)  (toplevel): import: /Users/timothee/git_clone/nim/Nim_prs/lib/system.nim [Processing]
Hint: (nims)  system: include: /Users/timothee/git_clone/nim/Nim_prs/lib/system/basic_types.nim [Processing]
Hint: (nims)  system: include: /Users/timothee/git_clone/nim/Nim_prs/lib/system/arithmetics.nim [Processing]
Hint: (nims)  system: include: /Users/timothee/git_clone/nim/Nim_prs/lib/system/comparisons.nim [Processing]
Hint: (nims)  system: include: /Users/timothee/git_clone/nim/Nim_prs/lib/system/inclrtl.nim [Processing]
Hint: (nims)  system: include: /Users/timothee/git_clone/nim/Nim_prs/lib/system/exceptions.nim [Processing]
Hint: (nims)  system: include: /Users/timothee/git_clone/nim/Nim_prs/lib/system/setops.nim [Processing]
Hint: (nims) > system: import: /Users/timothee/git_clone/nim/Nim_prs/lib/std/private/since.nim [Processing]

...
Hint: > (toplevel): import: /Users/timothee/git_clone/nim/Nim_prs/compiler/nim.nim [Processing]
Hint: >> nim: import: /Users/timothee/git_clone/nim/Nim_prs/lib/pure/os.nim [Processing]
Hint: >> os: include: /Users/timothee/git_clone/nim/Nim_prs/lib/system/inclrtl.nim [Processing]
Hint: >>> os: import: /Users/timothee/git_clone/nim/Nim_prs/lib/pure/strutils.nim [Processing]
Hint: >>>> strutils: import: /Users/timothee/git_clone/nim/Nim_prs/lib/pure/parseutils.nim [Processing]
Hint: >>>> parseutils: include: /Users/timothee/git_clone/nim/Nim_prs/lib/system/inclrtl.nim [Processing]
Hint: >>>> strutils: import: /Users/timothee/git_clone/nim/Nim_prs/lib/pure/math.nim [Processing]
Hint: >>>>> math: import: /Users/timothee/git_clone/nim/Nim_prs/lib/pure/bitops.nim [Processing]
Hint: >>>>>> bitops: import: /Users/timothee/git_clone/nim/Nim_prs/lib/core/macros.nim [Processing]
Hint: >>>>>> macros: include: /Users/timothee/git_clone/nim/Nim_prs/lib/system/inclrtl.nim [Processing]
Hint: >>>>> math: import: /Users/timothee/git_clone/nim/Nim_prs/lib/pure/fenv.nim [Processing]
Hint: >>>> strutils: import: /Users/timothee/git_clone/nim/Nim_prs/lib/pure/algorithm.nim [Processing]
...

full example

nim c --hint:all:off --warnings:off --processing:filenames --skipusercfg --skipparentcfg compiler/nim

• before PR
  https://gist.github.com/timotheecour/f9152b92c537596d04b2f08bf67f32ed

• after PR
  https://gist.github.com/timotheecour/af72c7f3f4cdeb039c2f8d2ab57c9776

[Araq]

Very nice.