Added option to force watch to use polling
Remove modernizr and use html5shiv.js directly.
Add respond.js so that media queries work in older IE too.
Only strip the drive name if it begins the string.
remove unused variables
align 'end' with 'def'
rename variable inside block
Add 1.5.1 to changelog.
Add 1.5.1 release post.
Update dat history in da site.
Fix path sanitization example in post. Props @gregose
Merge pull request #2178 from fabianrbz/remove_warnings
Update history to reflect merge of #2178 [ci skip]
Merge pull request #2175 from jekyll/security-yo
Update history to reflect merge of #2175 [ci skip]
Merge pull request #2165 from Zequez/master
Update history to reflect merge of #2165 [ci skip]
Merge pull request #2131 from XhmikosR/html5shiv
Update history to reflect merge of #2131 [ci skip]
remove duplicate code for tags and categories

Previously the `Site#tags` and `Site#categories` actually had the
same structure as a hash returned by `Site#post_attr_hash()`, but
maintained separately. Remove this duplicated infrastructure. For
backwards-compatibility for plugins, provide aliases for them.