Fix error in text formatter when note is nil
Version 1.8.10

Bugfix in text formatter
Require Chronic 0.10 series

It seems to fix at least one bug.

e.g. https://github.com/samg/timetrap/issues/74
Try to maintain compatibility with 1.8.7

Some non rubyist users are likely using system installed rubies that are
very old.  Try not to break timetrap for them just so they can get a
slightly better chronic.
Updated icalendar dependency to maintain Ruby 1.8.7 compatibility
Add test for resuming archived entry
Fall back on resuming archived entry
Bump version
add GitHub Flavored Markdown to README

* add syntax highlighting for Ruby
Merge pull request #78 from phlipper/patch-1

add GitHub Flavored Markdown to README