Add cpp linter (#64)

* Add c gcc option in the doc

* Add missing tag for eslint option in the doc

* Correct typo in doc (' ' instead of '.')

* add cpp linter

* correct typo in doc

* add filetype information for c++

ale_linters/cpp/gcc.vim

@@ -0,0 +1,23 @@
+" Author: geam <mdelage@student.42.fr>
+" Description: gcc linter for cpp files
+
+if exists('g:loaded_ale_linters_cpp_gcc')
+    finish
+endif
+
+let g:loaded_ale_linters_cpp_gcc = 1
+
+" Set this option to change the GCC options for warnings for C.
+if !exists('g:ale_cpp_gcc_options')
+    let g:ale_cpp_gcc_options = '-Wall'
+endif
+
+call ALEAddLinter('cpp', {
+\   'name': 'gcc',
+\   'output_stream': 'stderr',
+\   'executable': 'gcc',
+\   'command': 'gcc -S -x c++ -fsyntax-only '
+\       . g:ale_cpp_gcc_options
+\       . ' -',
+\   'callback': 'ale#handlers#HandleGCCFormat',
+\})