Amended and commented library functions

Commented all of the functions used.

Added to tablehelper:
table.contains(t, searchval) - returns true if searchval is in t
table.containskey(t, searchkey) - returns true if an element is in t
with key searchkey
table.sconcat() - concatenates all table elements with whitespaces

Added to stringhelper:
amended string.slice(str, from, to) - excepts optional arguments,
defaults from to 1 and to to #str.
Minor code changes

Nothing added, changed or fixed.