add functions: contains, index_of, last_index_of
fix support for strings in index_of and last_index_of
typos
where appropriate, automatically convert string values to keywords when the the string value is going to be used to check/sort against a map key
lol, wow this test was messed up
update 'contains' to allow checking for a substring in a string
add tests for contains, index_of and last_index_of