* CMake: add USE_PANDOC, USE_DOXYGEN options #101
* README: mention rust
* start integrating rust into build #101
* CMake: add USE_NETWORK option for cargo
* Debian: build-dep on doxygen
* rust: colloquy checks in Cargo.lock
* extract NCKEY defines into their own include
* colloquy: use clap to parse CLI args
* CMake: unify option namespace
* Python: update include path
* Rust: fix up --frozen workings for -DUSE_NETWORK=off
* CMake: abstract out colloquy a little
* Sync direct.hh to the New Way
Added:
* Plane: gradient (`ncplane_gradient`)
* Plane: gradient_sized (`ncplane_gradient_sized`)
* NotCurses: drop_planes (`ncplane_drop_planes`)
* NcReel: constructor which takes `Plane&`
* Visual: constructors which take `Plane const*`, `Plane&` and `Plane const&`)
* ncpp_build: a nonsensical "demo" which exists purely to test whether
the C++ builds and does absolutely nothing interesting.
Broke:
* All exceptions throw temporary objects instead of allocated
instances. Less typing in `catch` :P (and more conventional)
