5.3.0 release

* Revert "Don't rebuild unless .hl files are newer than output files".
  This reverts commit 15690b4ccb58d3e8efc7366e05b61d28ff45dbda.

* Use an in-memory cache to prevent unnecessary compilation of hoplon
  files, using last modified time to determine whether the source file
  has changed. This is enabled by default but can be disabled by setting
  the `:cache` option to `false` in the hoplon compiler options passed
  to the hoplon task (or directly to the compiler).

* The `:value` dispatch method for the `do!` multimethod had a bug
  wherein `(do! elem :value)` was setting the element's value to `nil`
  instead of getting the value.

* Add optional `interval` argument to `reload-js`, `reload-css`, and
  `reload-all` functions.