Make pins owned instead of mut borrowed

[kolen]

Currently, PCD8544 struct mutably borrows pins that it uses:

pcd8544/src/lib.rs

Lines 39 to 45 in fdaae48

	pub struct PCD8544<'a> {
	clk: &'a mut OutputPin,
	din: &'a mut OutputPin,
	dc: &'a mut OutputPin,
	ce: &'a mut OutputPin,
	rst: &'a mut OutputPin,
	light: &'a mut OutputPin,

While that might look like a good idea, putting these pins and PCD8544 to some struct is almost impossible in Rust's type system, requiring sophisticated hacks like rental or something based on Pin, which is high-end type system magic.

Most driver crates I've seen own pins.

This change is backwards-incompatible.

See also:

• https://internals.rust-lang.org/t/improving-self-referential-structs/4808
• https://stackoverflow.com/questions/32300132/why-cant-i-store-a-value-and-a-reference-to-that-value-in-the-same-struct

Same discussion in another your crate: kellerkindt/w5500#13

[kellerkindt]

Thanks! Sorry for the late response.
I'll upload a new version to crates.io in a few minutes, but I'll bump the version to 0.2.0 nonetheless... just to be extra explicit about the change :)