feat: Add more tags 

feat: Add `linkedin` icon Closes feathericons#77

feat: Add more tags to tags.json 

ci: Update .travis.yml 

docs: Update README.md 

feat: Update API BREAKING CHANGE: Each icon in the `feather.icons` object is now an `Icon` object with a `name`, `contents`, `tags` and `attrs` property. ```js /* BEFORE */ feather.icons.x // '<line ... /><line ... />' /* AFTER */ feather.icons.x // { // name: 'x', // contents: '<line ... /><line ... />`, // tags: ['cancel', 'close', 'delete', 'remove'], // attrs: { // class: 'feather feather-x', // xmlns: 'http://www.w3.org/2000/svg', // width: 24, // height: 24, // viewBox: '0 0 24 24', // fill: 'none', // stroke: 'currentColor', // 'stroke-width': 2, // 'stroke-linecap': 'round', // 'stroke-linejoin': 'round', // } // } ``` `feather.toSvg()` has been deprecated in favor of `feather.icons[name].toSvg()`: ```js /* BEFORE */ feather.toSvg('x') /* AFTER */ feather.icons.x.toSvg() ``` `feather.replace()` now copies all attributes on the placeholder element (i.e. `<i>`) to the `<svg>` tag instead of just `class` and `id`: ```html <i data-feather="circle" id="my-circle" class="foo bar" stroke-width="1"></i> <!-- <i> will be replaced with: <svg id="my-circle" class="feather feather-circle foo bar" xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1" stroke-linecap="round" stroke-linejoin="round"><circle cx="12" cy="12" r="10"></circle></svg> --> ```

feat: Updated replace() to pass id from placeholder element (featheri… …cons#193)

fix: Fix adding unwanted class 'null' 

fix: Fix `bold` icon 

feat: Add `underline` icon