Merge pull request #6 from takano-akio/size-t

PCRE_INFO_SIZE requires size_t *, not int *
Merge pull request #3 from takano-akio/cabal-readme-md

.cabal should mention README.md, not README
Precompile: remove an unsafe use of unsafePackCStringLen

The use of unsafePackCStringLen was unsafe because nothing
prevented the pcre object from garbage collected.