[file] new verbs 'isabsolute', 'normalize', 'cwd', 'patchpath'

[umlaeute]

this adds 4 new subcommands to [file]:

• [file normalize] - normalize a path by removing redundant components
• [file isabsolute] - check whether a path is absolute
  • Closes: add [file isabsolute] and/or [file isrelative] #1535
• [file cwd] - get/set the current working directory
  • Closes: add [file] verb (object) that returns current working directory #1537
• [file patchpath] - get the patch's path (kind of obsoletes the [dir( message to [pdcontrol])
  • Closes: add [file] verb (object) to resolve relative paths to current patch directory #1539

the file-help.pd reference has also been updated accordingly, which will most likely lead to conflicts with #1517.
i have first synched the reference patch with #1517 (as of 675591a), so i guess the resolution would be to use the file-help.pd of this PR.

[umlaeute]

out of mere habit this PR is based on develop...

[Spacechild1]

out of mere habit this PR is based on develop...

why not rebase onto master? ;-)

[umlaeute]

@millerpuckette what do you think about this? is this something that you do not want in principle? or that ought to be implemented differently? that needs more thinking?

has the ship sailed for new features in Pd-0.53?

note that this PR is actually driven by some requests by others (notably @Spacechild1; but also a few others chimed in)

[Spacechild1]

@millerpuckette It would be really great if this could make it into Pd 0.54!