Add support for cppcheck (#126)

* Add support for cppcheck

* Fix vint error in cppcheck handler

* Add vader test for CppCheck format handler

ale_linters/cpp/cppcheck.vim

@@ -0,0 +1,22 @@
+" Author: Bart Libert <bart.libert@gmail.com>
+" Description: cppcheck linter for cpp files
+
+if exists('g:loaded_ale_linters_cpp_cppcheck')
+    finish
+endif
+
+let g:loaded_ale_linters_cpp_cppcheck = 1
+
+" Set this option to change the cppcheck options
+if !exists('g:ale_cpp_cppcheck_options')
+    let g:ale_cpp_cppcheck_options = '--enable=style'
+endif
+
+call ale#linter#Define('cpp', {
+\   'name': 'cppcheck',
+\   'output_stream': 'both',
+\   'executable': 'cppcheck',
+\   'command': g:ale#util#stdin_wrapper . ' .cpp cppcheck -q --language=c++ '
+\       . g:ale_cpp_cppcheck_options,
+\   'callback': 'ale#handlers#HandleCppCheckFormat',
+\})