library: custom shader APIs

All works, but no support for uniforms yet.

src/library/README.md

@@ -1,8 +1,8 @@
 # Plugin Library
 This directory contains the source for the plugin library for RS3 (e.g. `libbolt-plugin.so`). If BOLT_SKIP_LIBRARIES is specified at build time, those libraries will not be built, and so the contents of this directory will be unused.
 
-All API documentation is in the form of a Texinfo document in doc.texi. The docs aren't touched by the build system, you need to generate them yourself using `texi2any` if you want to get them. Here's the command I use:
+All API documentation is in the form of a Texinfo document in doc.texi in the `doc` folder. The docs aren't touched by the build system, you need to generate them yourself using `texi2any` if you want to get them. Here's the command I use:
 
-```texi2any --html --no-split --no-number-sections --set-customization-variable='HIGHLIGHT_SYNTAX highlight' src/library/doc.texi```
+```texi2any --html --no-split --no-number-sections --set-customization-variable='HIGHLIGHT_SYNTAX highlight' src/library/doc/doc.texi```
 
 Alternatively the docs for the latest stable version can be found at https://bolt.adamcake.com/doc.