Spice up text formatter.

- Use custom format over time.Stamp
- Add colors to the Ctx keys (logrus inspired)
- Use fmt.Fprintf and bytes.Buffer for much more efficient string
  building.
factor out the logfmt formatting with optional coloring into a single function
add hotswap and speculative to ext package
add FuncHandler + more generic filter handler
syslog/ext use funchandler + gofmt
doc fixes + v2 refs
better doc example for filterhandler
ctxfilterhandler -> matchfilterhandler. add benchmarks. move back to canonical import paths, only support gopkg.in for release branches
update docs to point at v2
fix tests
add test for speculative handler + fix for bug
add test and fix + rename escalateerrhandler
extract term msg justification into constant and tune it down a little
make testing a little more reusable. add test for matchfilter on the common keys