DOCS, client API: add mpv release versions

The intention is to make it obvious which mpv releases certain changes
will apply to.

Also attempt to fix RST formatting of the list. This is not very proper,
but probably good enough.

DOCS/client-api-changes.rst

@@ -23,6 +23,7 @@ Also, read the section ``Compatibility`` in ``client.h``.
 API changes
 ===========
 
+```
  1.1    - remap dvdnav:// to dvd://
         - add "--cache-file", "--cache-file-size"
         - add "--colormatrix-primaries" (and property)
@@ -32,4 +33,6 @@ API changes
           insignificant is now significant
         - add "cache-free" and "cache-used" properties
         - OSX: the "coreaudio" AO spdif code is split into a separate AO
+--------- mpv 0.4.0 is released ---------
  1.0    - the API is declared stable
+```