Fix #8 use shiny::isTruthy on replacement in addin 

* Added "Library" button that opens a dialog to import regex patterns… … sourced from <https://projects.lukehaas.me/regexhub> and <https://github.com/trinker/qdapRegex>. The library is stored in `inst/extdata/patterns.json`. * Added "Introduction", "Try These Examples" and "Resources" tabs to the standard gadget Help tab. * Several bugfixes and tests were added around unicode character escaping within the gadget. * Enable `perl` mode by default in gadget (consistent with `stringr` and most regexes in the wild, but not base R). Write out selected options as comments when not consistent with base R when returning pattern from gadget. * Rewrote Readme with new screenshots and screencasts. * Added options `regexplain.addin.max_lines` and options for debugging gadget inputs.

Version 0.1.5 * Options from **Regex** tab are extended to **Output** tab as well. Colored options according to group where they are applied. * Added a mechanism to announce package updates while this package is on GitHub. Only checked once per R session on the first launch of the gadget.

Update news, docs, bump version 

v0.1.3 - Fixes css issues in view_regex() - Fixes unmatched groups in regex result

Version 0.1.0 -- addins and gadgets oh my Add addins and gadgets