Removed syntastic and replaced it with ale

Read more here:
https://github.com/w0rp/ale

sources_non_forked/ale/ale_linters/rust/rls.vim

@@ -0,0 +1,36 @@
+" Author: w0rp <devw0rp@gmail.com>
+" Description: A language server for Rust
+
+call ale#Set('rust_rls_executable', 'rls')
+call ale#Set('rust_rls_toolchain', 'nightly')
+
+function! ale_linters#rust#rls#GetExecutable(buffer) abort
+    return ale#Var(a:buffer, 'rust_rls_executable')
+endfunction
+
+function! ale_linters#rust#rls#GetCommand(buffer) abort
+    let l:executable = ale_linters#rust#rls#GetExecutable(a:buffer)
+    let l:toolchain = ale#Var(a:buffer, 'rust_rls_toolchain')
+
+    return ale#Escape(l:executable)
+    \   . ' +' . ale#Escape(l:toolchain)
+endfunction
+
+function! ale_linters#rust#rls#GetLanguage(buffer) abort
+    return 'rust'
+endfunction
+
+function! ale_linters#rust#rls#GetProjectRoot(buffer) abort
+    let l:cargo_file = ale#path#FindNearestFile(a:buffer, 'Cargo.toml')
+
+    return !empty(l:cargo_file) ? fnamemodify(l:cargo_file, ':h') : ''
+endfunction
+
+call ale#linter#Define('rust', {
+\   'name': 'rls',
+\   'lsp': 'stdio',
+\   'executable_callback': 'ale_linters#rust#rls#GetExecutable',
+\   'command_callback': 'ale_linters#rust#rls#GetCommand',
+\   'language_callback': 'ale_linters#rust#rls#GetLanguage',
+\   'project_root_callback': 'ale_linters#rust#rls#GetProjectRoot',
+\})