add struct for new submission

newSubmission contains the data needed to submit

Submitter interface also added (implemented by subreddit)
add submitID() func

returns the name of a subreddit, used for submitting
add Submit function

you can now submit both links and text posts through the API
add testing file

currently just tests the new Submit function
change Submit / add Captcha functions

changed parameters for Submit as subreddit no longer uses the submitter
interface, added captcha support
add tests for captcha
add CaptchaImage

gets an image that corresponds to the captcha iden returned by
NewCaptchaIden
remove function from the submitter interface

submitter interface no longer used
add captcha support / remove submitter interface

submissions can now be made that require captcha
Merge pull request #2 from scord/master

Add Submit function with testing