Add ability to filter output_http by headers/regex

Can filter output_http by percentage of requests, constistent with a specific header value (FNV32-a hash-based)
Can filter output_http to those with header matching a specific regexp
Can filter output_http to those whose URL matches a specfic regexp
Remove log statements
go fmt personal files
Further fmting
less, not greater
minor changes
Regex on string, not byte array
Update readme
Fix readme spacing
Documentation and test fixes
Add tests
Merge pull request #99 from mantasmatelis/filter-regex-and-header

Allow filtering by regex of URL or specific header, consistent filtering by hash of header