api: add some endpoints (&more)

libmxclient/API.md

@@ -0,0 +1,26 @@
+# libmxclient api doc
+
+C API
+
+simple highlevel matrix api intended for bindings to script languages
+
+`everything is a string`™
+
+this should make bindings easier.
+
+parameters are strings, either a simple name or json strings
+
+return values are either a strings starting with `ERR:` or a json result
+
+some funktions might return `SUCCESS.` as equivalent for `ret 0`
+
+returned strings must be free'ed y the caller
+
+it's the callers task to keep passed callback pointers alive
+
+## versions
+
+`v0` unstable, devolopment version
+
+all other version are stable, may get additions and security fixes, no other changes
+