(DOCUMENT-21) add docs for file_line to README.markdown

Without this, you have to look at the source file
(lib/puppet/type/file_line.rb) to know what it does. This adds that
documentation.
Remove trailing whitespace
Merge pull request #218 from mediatemple/remove_trailing_whitespace

Remove trailing whitespace
Fix strftime documentation in README

Markdown was barfing due to typo
Merge pull request #219 from petems/patch-1

Fix strftime documentation in README
Merge pull request #217 from teancom/fix/master/file_line

(DOCUMENT-21) add docs for file_line to README.markdown