Release 0.7.0

[Ghabry]

Imo we should add the "relevant for maintainers" release notes to the github release page and for the rest link to the blog post.

Suggested release notes:

For full release notes see: https://blog.easyrpg.org/2021/10/easyrpg-player-0-7-0-sword

## For Developers/Maintainers

The entire liblcf repository was restructured and everything moved into namespaces. E.g. instead of Actor the class is now called lcf::rpg::Actor. This also improves the error reporting because you can see directly where the error occured from. (#342, #361)

The GNU compiler extensions are enabled now if supported. These are required by certain ports such as AmigaOS. (#366)

Building with gcc5 works again. (#374)

Expat 2.2.10 and newer are now supported by the CMake build system (#385)

The supported versions of CMake are now 3.10 and newer (#422)

Using liblcf from CMake does not require pkg-config anymore. (#431)