Refactor repository layout and convert build system to Mage.

This commit implements a massive refactor of the repository, and
moves the build system over to use Mage (magefile.org) which should
allow seamless building across multiple platforms.

tools/vendor/github.com/alecthomas/gometalinter/README.md

@@ -3,10 +3,13 @@
 
 <!-- MarkdownTOC -->
 
+- [Installing](#installing)
 - [Editor integration](#editor-integration)
 - [Supported linters](#supported-linters)
 - [Configuration file](#configuration-file)
-- [Installing](#installing)
+    - [`Format` key](#format-key)
+    - [Format Methods](#format-methods)
+  - [Adding Custom linters](#adding-custom-linters)
 - [Comment directives](#comment-directives)
 - [Quickstart](#quickstart)
 - [FAQ](#faq)
@@ -39,6 +42,16 @@ eg.
 
 It is intended for use with editor/IDE integration.
 
+## Installing
+
+There are two options for installing gometalinter.
+
+1. Install a stable version, eg. `go get -u gopkg.in/alecthomas/gometalinter.v2`.
+   I will generally only tag a new stable version when it has passed the Travis
+  regression tests. The downside is that the binary will be called `gometalinter.v2`.
+2. Install from HEAD with: `go get -u github.com/alecthomas/gometalinter`.
+   This has the downside that changes to gometalinter may break.
+
 ## Editor integration
 
 - [SublimeLinter plugin](https://github.com/alecthomas/SublimeLinter-contrib-gometalinter).
@@ -91,9 +104,11 @@ Additional linters can be added through the command line with `--linter=NAME:COM
 
 ## Configuration file
 
-gometalinter now supports a JSON configuration file which can be loaded via
-`--config=<file>`. The format of this file is determined by the `Config` struct
-in [config.go](https://github.com/alecthomas/gometalinter/blob/master/config.go).
+gometalinter now supports a JSON configuration file called `.gometalinter.json` that can
+be placed at the root of your project. The configuration file will be automatically loaded
+from the working directory or any parent directory and can be overridden by passing
+`--config=<file>` or ignored with `--no-config`. The format of this file is determined by
+the `Config` struct in [config.go](https://github.com/alecthomas/gometalinter/blob/master/config.go).
 
 The configuration file mostly corresponds to command-line flags, with the following exceptions:
 
@@ -110,6 +125,27 @@ Here is an example configuration file:
 }
 ```
 
+If a `.gometalinter.json` file is loaded, individual options can still be overridden by
+passing command-line flags. All flags are parsed in order, meaning configuration passed
+with the `--config` flag will override any command-line flags passed before and be
+overridden by flags passed after.
+
+
+#### `Format` key
+
+The default `Format` key places the different fields of an `Issue` into a template. this
+corresponds to the `--format` option command-line flag.
+
+Default `Format`:
+```
+Format: "{{.Path}}:{{.Line}}:{{if .Col}}{{.Col}}{{end}}:{{.Severity}}: {{.Message}} ({{.Linter}})"
+```
+
+#### Format Methods
+
+* `{{.Path.Relative}}` - equivalent to `{{.Path}}` which outputs a relative path to the file
+* `{{.Path.Abs}}` - outputs an absolute path to the file
+
 ### Adding Custom linters
 
 Linters can be added and customized from the config file using the `Linters` field.
@@ -138,16 +174,6 @@ Example:
 $ gometalinter --linter='vet:go tool vet -printfuncs=Infof,Debugf,Warningf,Errorf:PATH:LINE:MESSAGE' .
 ```
 
-## Installing
-
-There are two options for installing gometalinter.
-
-1. Install a stable version, eg. `go get -u gopkg.in/alecthomas/gometalinter.v1`.
-   I will generally only tag a new stable version when it has passed the Travis
-  regression tests. The downside is that the binary will be called `gometalinter.v1`.
-2. Install from HEAD with: `go get -u github.com/alecthomas/gometalinter`.
-   This has the downside that changes to gometalinter may break.
-
 ## Comment directives
 
 gometalinter supports suppression of linter messages via comment directives. The