Write error list for commented signals

Fix `+IsA<Object>` without active signals in gesture.rs

Signals

Add skip_assert_init macro calls to enums/flags codegen

Allow forcing generation of a trait when it's only needed by other crates

Add Shared (refcounted) records support

Generate bitflags and enums in high-level crates

Use rust_type when generating `Foo::uninitialized()` chunks

... to account for types that come from external crates.

Make record returns nullable by default, small tweaks

The macro always implements that relationship anyway

Use more expressive object macro syntax for cross-crate inheritance

Change version features format from "x.y" to "vx_y" to make crates.io happy

Add higher_crate_name to rename gobject and gio to glib

Set higher_crate_name for "gobject" and "gio" to "glib".

Docs: include Since and deprecated versions, `[Deprecated]` tags

...into struct and trait docs.
Drop alias docs.

If all class/interface/record functions have a `version`, assume it has
the same one. Same with ...

Small doc improvements

Order types in the docs alphabetically

Docs generator extensions and class hierarchy refactoring

Appveyor: speed up libgit2-sys build

sys build script: avoid duplicate metadata when it's not suppressed

More intelligent symbol name handling and other docs generator improvements

Build script update