Safe Rust bindings for libvips

For the moment, this crate requires libvips 8.13 or higher to be installed on the system.

To-do

vips-sys

• Fix warning: 'extern' block uses type 'u128', which is not FFI-safe
• Create Allowlist for FFI bindings

vips-rs

• Complete the wrapper for VipsImage
  • Constructors
  • Image output
  • Image properties
  • [] and () operators as per the C++ bindings?
• Generate operators (via macro?)
  • Define macro
  • Generate all operators
• Abstract away VIPS_INIT and vips_shutdown as much as possible
  • vips_init() -> Result<_,_>
  • VipsHandle
  • ensure_vips_init_or_exit()
  • vips_main decorator macro (vips_init_or_exit before fn, vips_shutdown after)
• Merge vips_sys and vips_rs (this repo)
• Write rudimentary test suite
  • leak checks
  • basic functionality checks
• Un-ignore doctests and make them pass
• Ship Vips with this crate
• Publish crate