Add new method on job.go to get builds fields with filter

[Fuerback]

In this PR is included a new method GetBuildsFieldsWithFilter on job.go which is a copy of GetBuildsFields but using the API filters.

For array-type properties, a range specifier is supported. For example, tree=jobs[name]{0,10} would retrieve the name of the first 10 jobs. The range specifier has the following variants:

• {M,N}: From the M-th element (inclusive) to the N-th element (exclusive).
• {M,}: From the M-th element (inclusive) to the end.
• {,N}: From the first element (inclusive) to the N-th element (exclusive). The same as {0,N}.
• {N}: Just retrieve the N-th element. The same as {N,N+1}.

I also executed the commands below:

go fmt ./...
goimports -l -w .

And that's why there are so many small changes, such as import orders, comments, and godoc space.