Update README.markdown
Merge pull request #114 from victorguo/patch-1

Update README.markdown
Changed some wording to clear up confusion with regards to FMDatabaseQueue
Might want to call those asserts before an abort()…
Lazily populate columnNameToIndexMap when accessing so that clients can use the value without causing setupColumns to be called first.
Fix for issue #118 (thanks @Kelp404!)
Merge branch 'master' of https://github.com/bandcampdotcom/fmdb
Cleanup of some code + notes on what is going on