In order to make the Si5351 configurable add some needed assets,
create the ability to print the frequency with selected digits and add
a channel screen.
Create `print_u8()` helper function to print `u8` primitives to
lcd. Refactor contrast and backlight variables to also keep them in a
global `AtomicU8`.
To reduce length of `main.rs` and therefor improve readability create
source files for:
- Assets (`assets.rs`): Contains all graphical assets such as the
splash screen assets, symbols and the symbol table.
- LCD (`lcd.rs`): Contains all lower level things regarding the LCD
such as the `Lcd` struct and its implementations.
- Screen (`screen/mod.rs`):
- Splash (`screen/splash.rs`)
- Home (`screen/home.rs`)
- Setup (`screen/setup.rs`)
In the future it would probably make sense to move the LCD module into
the screen module.
To create a setup screen more symbols are created and added to the
symbol table. Helper functions are added to draw homogenous areas onto
the display. Add two new fields `Click` and `Back` to the `Input`
enum. Adapt functions already handling input to those new kinds of
input. Add the setup screen construct. Add global atomics to handle
the button and the timer for handling the back input when the button
is pressed until the timer one overflows. Button press and the timer
are handled via interrupts.
Add several symbols and a symbol table in an ascii order. Add the
`print()` and `print_inverted()` functions to be able to draw strings,
"black on white" as well as "white on black" onto the display. Add a
`HomeScreen` which also saves the state of which selection is
active. To save the screen state and also make it accessible globally
use a `RefCell` contained in a `Mutex`.
Also update the build dependencies.
It has to be decided what kind of tooling should be used, for now
cargo-make is used. This will probably be changed to use the tools
provided by [probe.rs](https://probe.rs).
