Created addValidater function in iz, and validator.

addValidator adds to the validator object.  when called from iz, will
add it to the current instance of iz, and to the validator.  Created
tests. Updated documentation.

If the validator already exists will not override, unless told to.
Fixed spelling and wording in README.md
Merge pull request #23 from timmckenzie/master

Created addValidater function in iz, and validator.