Removed syntastic and replaced it with ale

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

sources_non_forked/ale/ale_linters/rust/rustc.vim

@@ -0,0 +1,33 @@
+" Author: Daniel Schemala <istjanichtzufassen@gmail.com>
+" Description: rustc for rust files
+
+call ale#Set('rust_rustc_options', '-Z no-trans')
+
+function! ale_linters#rust#rustc#RustcCommand(buffer) abort
+    " Try to guess the library search path. If the project is managed by cargo,
+    " it's usually <project root>/target/debug/deps/ or
+    " <project root>/target/release/deps/
+    let l:cargo_file = ale#path#FindNearestFile(a:buffer, 'Cargo.toml')
+
+    if l:cargo_file isnot# ''
+        let l:root = fnamemodify(l:cargo_file, ':h')
+        let l:dependencies = ' -L ' . ale#Escape(ale#path#GetAbsPath(l:root, 'target/debug/deps'))
+        \   . ' -L ' . ale#Escape(ale#path#GetAbsPath(l:root, 'target/release/deps'))
+    else
+        let l:dependencies = ''
+    endif
+
+    let l:options = ale#Var(a:buffer, 'rust_rustc_options')
+
+    return 'rustc --error-format=json'
+    \   . (!empty(l:options) ? ' ' . l:options : '')
+    \   . l:dependencies . ' -'
+endfunction
+
+call ale#linter#Define('rust', {
+\   'name': 'rustc',
+\   'executable': 'rustc',
+\   'command_callback': 'ale_linters#rust#rustc#RustcCommand',
+\   'callback': 'ale#handlers#rust#HandleRustErrors',
+\   'output_stream': 'stderr',
+\})