tidy comments
add fallback if user has javascript disabled
add new setting to show image in feed

This setting is optional, and off by default. Since the image is not actually
part of the entry content, this would add it to the beginning of the post if the
post thumbnail is set.
add rss output functions

Checks Settings > Reading. If full text is selected, large image is added to entry content.
If Send Images to RSS plugin is active, email size image is added to entry content.
If Summary is selected, thumbnail is added to description (excerpt).
add rss function
validate feed_image
add help text
modify feed output if featured image exists in post
clarify docblock on new seting
add function to check/update new setting

since feed_image is a new setting in the array, there is an error if it's not set for users
upgrading from 1.4.3. this function checks if it isn't there and if it's not, adds it.

for new users, there is no need to check.
add class for RSS work

extracted RSS filters from output class and created new RSS class.
refactored rss class

First check is now full text as that is more standard. Reorganized decision process,
and properly accounted for optional alternate feed in Send Images to RSS.
updated readme
updated version to 1.5.0