add regexp support

[ryancdotorg]

• Hostnames starting with ~ will be treated as regular expressions - queries will be lowercased before matching.
• Globs remain supported.
• /blockcache/* API calls can now list/remove regular expression and glob hosts
• MemoryBlockCache.Special reworked as a map of *regexp.Regexps, with nil for simple globs

Example entry for blocking instart logic g00 hosts:

~^[0-9a-z-]+[.]g00[.]

Having a lot of glob/regexp entries blocked may be slow, try to use sparingly.

Fixes #35