RFC: new benchmark command

[philpep]

Currently we have asv rm to remove specific benchmark results.

What about a new benchmark command that could handle:

• benchmark and results listing
• filter results by benchmark name/regexp, params, date range, individual commit, commit range
• actions (rename, remove)

[pv]

I think commands for displaying and more operations on benchmarks could be useful.
Eg. #450

However, if rm and compare are top-level commands, should the new ones not be also top-level commands?
In any case, it's probably best to avoid adding duplicated functionality.