Implement Lua ALE setup & overhaul documentation

1. Add ale.setup and ale.setup.buffer for pure Lua configuration.
2. Update many global settings to use Booleans instead of numbers to
   make types easiert to work with in Lua.
3. Radically reformat documentation and fix errors to make
   documentation more usable for Neovim users.

doc/ale-swift.txt

@@ -18,20 +18,22 @@ There are 3 options to enable linting and fixing with Apple's swift-format:
 Additionally, ALE tries to locate and use the nearest existing `.swift-format`
 configuration file.
 
-
-g:ale_swift_appleswiftformat_executable
+                                *ale-options.swift_appleswiftformat_executable*
                                       *g:ale_swift_appleswiftformat_executable*
                                       *b:ale_swift_appleswiftformat_executable*
+swift_appleswiftformat_executable
+g:ale_swift_appleswiftformat_executable
   Type: |String|
   Default: `'swift-format'`
 
   This variable can be modified to change the executable path for
   `swift-format`.
 
-
-g:ale_swift_appleswiftformat_use_swiftpm
+                               *ale-options.swift_appleswiftformat_use_swiftpm*
                                      *g:ale_swift_appleswiftformat_use_swiftpm*
                                      *b:ale_swift_appleswiftformat_use_swiftpm*
+swift_appleswiftformat_use_swiftpm
+g:ale_swift_appleswiftformat_use_swiftpm
   Type: |Number|
   Default: `0`
 
@@ -54,9 +56,11 @@ sourcekitlsp                                           *ale-swift-sourcekitlsp*
 To enable the SourceKit-LSP you need to install and build the executable as
 described here: https://github.com/apple/sourcekit-lsp#building-sourcekit-lsp
 
-
-g:ale_sourcekit_lsp_executable                 *g:ale_sourcekit_lsp_executable*
+                                         *ale-options.sourcekit_lsp_executable*
+                                               *g:ale_sourcekit_lsp_executable*
                                                *b:ale_sourcekit_lsp_executable*
+sourcekit_lsp_executable
+g:ale_sourcekit_lsp_executable
   Type: |String|
   Default: `'sourcekit-lsp'`