Release v0.1.0

This represents the initial release, mostly so we can get VLC with basic
libplacebo support out of the way.

As of v0.1, libplacebo only supports vulkan, and only exposes the
low-level interfaces (dispatch, shader, ra). So as of now, libplacebo is
only useful either as a GLSL shader generator (shaders.h), or as an
offline tool for processing images (dispatch.h + vulkan). There is
currently no high-level image/video rendering interface, and no support
for OpenGL whatsoever.

OpenGL support is planned for v0.2, and the addition of a high level
renderer is planend for v0.3.
This tag has no release notes.