vdoc: rewrite and extend vdocignore

[ttytm]

After working on an improved status quo to also have a good fallback, this PR approaches to rewrite and to extend .vdocignore.

• It adds pattern support.

  Until now to ignore a and the same pattern in a sub-directory (b/a) it is required to set the exact path for every subdirectory. Now it is sufficient to set the pattern

Ignore Goal	Current	Updated
a a/b b/c/a	a a/b b/c/a	a

• Similar to gitignore a pattern starting with / will be treated as relative pattern.
  -> /a will ignore /a but not /b/a.
  -> /c/d will ignore /c/d but not /b/c/d

• Treats lines starting with # as comments

• Removes the functionality that an empty ignore file ignores all in its directory.

[JalonSolov]

Would be nice, of course, to get full .gitignore paths, so you could have

**/a/

meaning every a subdir... /a, /b/a, /1/2/3/4/5/6/7/a, etc.

At the very least, support trailing slash means subdir, while no trailing slash means file.

[ttytm]

Agree about the wildcards. Would approach it at a later point, or if someone else does it it's cool as well.
Tho in a gitignore it's not that only a trailing slash means a directory, a dir is also true for a pattern without a trailing slash.

[JalonSolov]

Yep, but a trailing slash forces it to only match subdirs.

[ttytm]

Yep, but a trailing slash forces it to only match subdirs.

Yep, a test for this is added.

To give more info: Our .vdocignore is in general a little simpler then a .gitignore since it only looks for modules that end with .v. So the test has an ignore pattern name.v/, a directory with the name name.v and also file name.v, testing that only the directory is ignored.