Add support for Scala

From https://github.com/kien/ctrlp.vim/pull/590:

> Buffer tags supported includes traits, methods, types, classes, objects, packages. In order to use this with Exuberant Ctags, the following needs to be added to ~/.ctags:

```
--langdef=Scala
--langmap=Scala:.scala
--regex-scala=/^[ \t]*((abstract|final|sealed|implicit|lazy)[ \t]*)*(private|protected)?[ \t]*class[ \t]+([a-zA-Z0-9_]+)/\4/c,classes/
--regex-scala=/^[ \t]*((abstract|final|sealed|implicit|lazy)[ \t]*)*(private|protected)?[ \t]*object[ \t]+([a-zA-Z0-9_]+)/\4/c,objects/
--regex-scala=/^[ \t]*((abstract|final|sealed|implicit|lazy)[ \t]*)*(private|protected)?[ \t]*case class[ \t]+([a-zA-Z0-9_]+)/\4/c,case classes/
--regex-scala=/^[ \t]*((abstract|final|sealed|implicit|lazy)[ \t]*)*(private|protected)?[ \t]*case object[ \t]+([a-zA-Z0-9_]+)/\4/c,case objects/
--regex-scala=/^[ \t]*((abstract|final|sealed|implicit|lazy)[ \t]*)*(private|protected)?[ \t]*trait[ \t]+([a-zA-Z0-9_]+)/\4/t,traits/
--regex-scala=/^[ \t]*type[ \t]+([a-zA-Z0-9_]+)/\1/T,types/
--regex-scala=/^[ \t]*((abstract|final|sealed|implicit|lazy)[ \t]*)*def[ \t]+([a-zA-Z0-9_]+)/\3/m,methods/
--regex-scala=/^[ \t]*((abstract|final|sealed|implicit|lazy)[ \t]*)*val[ \t]+([a-zA-Z0-9_]+)/\3/l,constants/
--regex-scala=/^[ \t]*((abstract|final|sealed|implicit|lazy)[ \t]*)*var[ \t]+([a-zA-Z0-9_]+)/\3/l,variables/
--regex-scala=/^[ \t]*package[ \t]+([a-zA-Z0-9_.]+)/\1/p,packages/
```