fix typos
add substring (with an alias to subs)
remove old test namespace
show failing expression and result in assert=
provide a friendlier variant of assert

similar to assert=
add missing IMeta extend for PersistentList
add -> and ->>
add last and butlast
implement meta/with-meta on sets
merge branch 'master' into stdlib-improvements
Merge pull request #54 from heyLu/stdlib-improvements

Stdlib improvements