Remove symlinking

[eliasmalik]

Related to #248

So thanks to #267 I finally got round to writing enough tests for this to be worth PR-ing.

Major Changes

• Post-install script removed; default behaviour on install no is no longer to create a symlinked .eslintrc.js file
• CLI flag --link added to still allow symlink to be generated if user wishes
• Tests added for --link and --fix flags

Minor Changes

• README updated to explain --link and --fix usage

Not a particularly urgent PR. Also I'm thinking this PR should bump us up to 1.2.0 rather than 1.1.5 since its a change in behaviour, but open to suggestions.

[nelsonic]

@eliasCodes code looks good. thanks for making the time to update this. 👍
Please publish a new version on using the following:

git checkout master
git pull
npm version minor -m 'make symlink optional - no functional changes'
git push && git push --tags
npm publish

[eliasmalik]

@nelsonic done 👍