Add CMake option C3_ENABLE_CLANGD_LSP (#1414)

* CMake option C3_ENABLE_CLANGD_LSP

The CMake option enables the generation of compile_commands.json in
the build directory and the creation of a symlink in the root
directory targeting the new file,
this will allow the Clangd Language Server Protocol (LSP) to
function properly.

* Added .editorconfig

EditorConfig helps maintain consistent coding styles:
https://editorconfig.org/

.editorconfig

@@ -0,0 +1,28 @@
+# EditorConfig is awesome: https://editorconfig.org
+
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+
+[CMakeLists.txt]
+indent_style = space
+indent_size = 4
+
+[*.{c,cc,h}]
+indent_style = space
+indent_size = 4
+
+[*.{c3}]
+indent_style = space
+indent_size = 4
+
+[*.{json,toml,yml,gyp}]
+indent_style = space
+indent_size = 2
+
+[*.{py,pyi}]
+indent_style = space
+indent_size = 2
+