[TW-1585] Ability to match subprojects

_Renato Alves on 2015-03-27T16:30:29Z says:_

As discussed in IRC with Paul and referencing David Patrick which may have raised this issue the first time.

It is sometimes impossible to match subprojects without potentially including tasks from other projects.

This is what currently happens when trying to match only tasks from subproject "two":
```
$ task add proj:one.two 1
$ task add proj:one.twos 2
$ task add proj:one.two.three 3
$ task add proj:one.twos.three 4
$ task add proj:one_two 5
$ task add proj:two 6

$ task list proj:two
1 match

$ task list proj.has:two
6 matches

$ task list proj:one.two
(proj:one_two not matched)
4 matches

$ task list proj.has:one.two
(proj:one_two matched, dot treated as wildcard)
5 matches
```

This feature request proposes using 'dot' to indicate that we are searching for subprojects and the boundaries of the subproject name.
```
1. Leading dot
$ task list proj:.two
ID Project Description
1 one.two 1
2 one.twos 2
3 one.two.three 3
4 one.twos.three 4
1. Leading and trailing dot
$ task list proj:.two.
ID Project Description
1 one.two 1
3 one.two.three 3
```