Update README.md

Update benchmarks

Merge pull request #4 from lestrrat/topic/optimized-func

Update benchmarks

Optimize the no functional version

Merge pull request #3 from lestrrat/topic/single-percent

return error on stray %

Merge pull request #2 from lestrrat/topic/exclusion

add to exclusion pattern

Update README.md

Update benchmark

Oh yeah, writing out a string is MUCH faster than writing to an io.Writer

this doesn't really change anything, but we get to save on a closure

tweak FormatString()

Use append instead of write