fix a readme typo
fix another readme typo
js performance improvement + typo fixes

* improve js performance by caching the `.custom-metadata-field` selector
* rename all jQuery events to `custom_metadata` as opposed to `custom-metada`
* add a missing semi-colon
js performance improvements + typo fixes

* improve js performance by caching the `.custom-metadata-field` selector
* rename all jQuery events to `custom_metadata` as opposed to `custom-metada`
more js improvements

* improve js performance by caching the `.custom-metadata-field` selector
* rename all jQuery events to `custom_metadata` as opposed to `custom-metada`
* fix missing semi-colon
add new field `link` field type

adds a new link field type that uses the WordPress core link dialog/UI

props PhilippSchreiber for initial work on this
fixes #29
css for link file type

ref #29
update jQuery smoothness UI

update jQuery smoothness UI to latest version and add specificity to most selectors so that it only affects the date picker field, otherwise it conflicts with WordPress' built-in styles for the link manager