Update docker image to use 0.3.6
Add hasPrefix(prefix,s) and hasSuffix(suffix,s)
List functions in FuncMap and README.md alphabetically
Add trimPrefix(prefix,s) and trimSuffix(suffix,s)
Merge pull request #40 from md5/add-prefix-suffix-functions

Add functions to handle string prefixes and suffixes
Fix typo in test name
Add "keys" function
Document "keys" function