Referencing the documentation for jekyll-import installation

Currently, there are only beta releases of the jekyll-import gem, so to
install it, you have to do `gem install jekyll-import --pre`. Instead
of giving instructions that don't work right now, reference the
documentation. That way, this doesn't need to be updated again when
jekyll-import has a non-beta version; just the documentation will need
updating.
Prepare for a 1.3.0.rc release
Merge pull request #1662 from carols10cents/fix-import-error-message

Add `--pre` to the recommended command to install jekyll-import.
Update history to reflect merge of #1662
Fix a typo.
Add Asset Path Tag to plugin list in docs

Requested by @mattr-
https://github.com/mojombo/jekyll/issues/881#issuecomment-27276509
Add Jekyll 1.3.0.rc1 Release Post to Gemspec
Merge pull request #1667 from mojombo/release-1.3.0.rc

Prepare for a 1.3.0.rc release
Release 1.3.0.rc
add missing section info to the drafts post, in order to make navigation links (Back, Next) work
Merge pull request #1677 from yizeng/add-section-info-to-drafts

add missing section info to the drafts post
Use the proper date in the gemspec
Update history to reflect merge of #1677
Update implementation of listen for v1.3.x
Merge pull request #1687 from mojombo/fix-listen

Fix implementation of listen for v1.3.x
Update history to reflect merge of #1687
updated end to endfor
Merge pull request #1691 from katydecorah/master

updated end to endfor
Update history to reflect merge of #1691
Prep for the 1.3.0 release