feat: common module options (show_if, on_click, tooltip)

The first three of many options that are common to all modules.

Resolves #36. Resolves partially #34.

docs/Scripts.md

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+There are various places inside the configuration (other than the `script` module)
+that allow script input to dynamically set values.
+
+Scripts are passed to `sh -c`.
+
+Two types of scripts exist: polling and watching:
+
+- Polling scripts will run and wait for exit.
+  Normally they will repeat this at an interval, hence the name, although in some cases they may only run on a user
+  event.
+  If the script exited code 0, the `stdout` will be used. Otherwise, `stderr` will be printed to the log.
+- Watching scripts start a long-running process. Every time the process writes to `stdout`, the last line is captured
+  and used.
+
+One should prefer to use watch-mode where possible, as it removes the overhead of regularly spawning processes.
+That said, there are some cases which only support polling. These are indicated by `Script [polling]` as the option
+type.
+
+## Writing script configs
+
+There are two available config formats for scripts, shorthand as a string, or longhand as an object.
+Shorthand can be used in all cases, but there are some cases (such as embedding scripts inside strings) where longhand
+cannot be used.
+
+In both formats, `mode` is one of `poll` or `watch` and `interval` is the number of milliseconds to wait between
+spawning the script.
+
+Both `mode` and `interval` are optional and can be excluded to fall back to their defaults of `poll` and `5000`
+respectively.
+
+### Shorthand (string)
+
+Shorthand scripts should be written in the format:
+
+```
+mode:interval:script
+```
+
+For example:
+
+```
+poll:5000:uptime -p | cut -d ' ' -f2-
+```
+
+### Longhand (object)
+
+An object consisting of the `cmd` key and optionally the `mode` and/or `interval` keys.
+
+<details>
+<summary>JSON</summary>
+
+```json
+{
+  "mode": "poll",
+  "interval": 5000,
+  "cmd": "uptime -p | cut -d ' ' -f2-"
+}
+```
+</details>
+
+<details>
+<summary>YAML</summary>
+
+```yaml
+mode: poll
+interval: 5000
+cmd: "uptime -p | cut -d ' ' -f2-"
+```
+</details>
+
+<details>
+<summary>YAML</summary>
+
+```toml
+mode = "poll"
+interval = 5000
+cmd = "uptime -p | cut -d ' ' -f2-"
+```
+</details>
+
+<details>
+<summary>Corn</summary>
+
+```corn
+{
+  mode = "poll"
+  interval = 5000
+  cmd = "uptime -p | cut -d ' ' -f2-"
+}
+```
+</details>