Switch library documentation to gi-docgen

Switch from gtk-doc to gi-docgen for the library documentation and
adjust the source files accordingly.

We don't bother about the daemon doc headers as they're not built into
any docs atm.

Closes: #56

doc/build-howto.md

@@ -0,0 +1,57 @@
+Title: Compiling with libfeedback
+Slug: building
+
+# Compiling with libfeedback
+
+If you need to build libfeedback, get the source from
+[here](https://source.puri.sm/Librem5/feedbackd) and see the `README.md` file.
+
+## Using `pkg-config`
+
+Like other GObject based libraries, libfeedback uses `pkg-config` to provide compiler
+options. The package name is `libfeedback-0.0`.
+
+When using the Meson build system you can declare a dependency like:
+
+```meson
+dependency('libfeedback-0.0')
+```
+
+## Bundling the Library
+
+### Using a Subproject
+
+Libfeedback can be used as a Meson subproject.  Create a
+`subprojects/libfeedback.wrap` file with the following contents:
+
+```ini
+[wrap-git]
+directory=libfeedback
+url=https://source.puri.sm/Librem5/feedbackd.git
+revision=main
+depth=1
+```
+
+Add this to your `meson.build`:
+
+```meson
+libfeedback = dependency(
+  'libfeedback-0.0',
+  version: '>= 0.0.1',
+  fallback: ['libfeedback', 'libfeedback_dep'],
+  default_options: [
+    'daemon=false',
+    'man=false',
+    'gtk_doc=false',
+    'vapi=false',
+    'tests=false',
+  ]
+)
+```
+
+Then the `libfeedback` variable can be used as a dependency.
+
+# Next Steps
+
+Once libfeedback has been compiled and included into your project, it needs to be
+initialized. See [Initialization](initialization.html).