Clojure Support via Eastwood

Was wondering if would be possible to get Clojure linting support in Ale.

There is a lint tool for Clojure called [Eastwood](https://github.com/jonase/eastwood). To make use of it, a user needs to simply have `{:user {:plugins [[jonase/eastwood "0.2.5"]] }}` in the `$HOME/.lein/profiles.clj` file, and call `lein eastwood` while in the directory that has the file they want to lint.

Looking through the `ale_linters` directory, I have a _vague_ idea on how to create a proper `.vim` file to make use of Eastwood in Ale. But if it's more than just the common pattern I see in all the `linter.vim` files, then it might be a bit more difficult for me to do.

EDIT: Apologies, to clarify what the `lein eastwood` command does

> [Runs] Eastwood with the default set of lint warnings on all of the Clojure files in the source and test paths of your project

Start by comparing the existing files in the ale_linters directory, especially the common linter.vim pattern, with Eastwood's lein eastwood command. Verify the command in a Clojure project containing source and test files; done means Ale can invoke Eastwood and report its lint warnings.

Written by the indexing model from the issue text.