Add support for fatou (#5159)

Add a linter that runs the fatou language server (`fatou lsp`) for Julia
diagnostics, and a fixer that formats Julia with `fatou format`.

ale_linters/julia/fatou.vim

@@ -0,0 +1,18 @@
+" Author: Johan Larsson <johan@jolars.co>
+" Description: A language server, formatter, and linter for Julia
+
+call ale#Set('julia_fatou_executable', 'fatou')
+
+function! ale_linters#julia#fatou#GetProjectRoot(buffer) abort
+    let l:config = ale#path#FindNearestFile(a:buffer, 'fatou.toml')
+
+    return !empty(l:config) ? fnamemodify(l:config, ':h') : ''
+endfunction
+
+call ale#linter#Define('julia', {
+\   'name': 'fatou',
+\   'lsp': 'stdio',
+\   'executable': {b -> ale#Var(b, 'julia_fatou_executable')},
+\   'command': '%e lsp',
+\   'project_root': function('ale_linters#julia#fatou#GetProjectRoot'),
+\})