Theorem environments in Typst with minimal fuss.

To use, import and add a show rule:

```
#import "@preview/minienvs:0.1.0": *
#show: minienvs
```

You can optionally pass a custom configuration in the show-rule via `minienvs.with(…)`

(see Customization).

You can now just add a theorem along with its proof using the term list syntax. For example:

```
/ Theorem (Ville's inequality):
Let $X_0, ...$ be a non-negative supermartingale. Then, for any real number $a > 0$,
$ PP[sup_(n>=0) X_n >= a] <= EE[X_0]/a. $
Let us now prove it:
/ Proof:
Consider the stopping time $N = inf {t >= 1 : X_t >= a}$.
By the optional stopping theorem and the supermartingale convergence theorem, we have that
$
EE[X_0] >= EE[X_N]
&= EE[X_N | N < oo] PP[N < oo] + EE[X_oo | N = oo] PP[N = oo] \
&>= EE[X_N | N < oo] PP[N < oo]
= EE[X_N/a | N < oo] a PP[N < oo]. \
$
And, therefore,
$ PP[N < oo] <= EE[X_0] \/ a EE[X_N/a | N < oo] <= EE[X_0] \/ a. $
```

## Labels and references

Currently, in order to label a minienv one needs to use the `envlabel`

function. For example:

```
/ Lemma (Donsker and Varadhan's variational formula) #envlabel(<change-of-measure>):
For any measureable, bounded function $h : Theta -> RR$ we have:
$ log EE_(theta ~ pi)[exp h(theta)] = sup_(rho in cal(P)(Theta)) [ EE_(theta~rho)[h(theta)] - KL(rho || pi) ]. $
As we will see, @change-of-measure is a fundamental building block of PAC-Bayes bounds.
```

## Customization

You can customize the appearance of minienvs by providing a configuration to the show-rule. For example, for the default configuration, you can do:

```
#show: minienvs.with(config: (
// Whether to give numbers for environments.
// If the environment is not mentioned in this dict, it has a number.
no-numbering: (
proof: true,
),
// Additional options for the `block` containing the minienv (e.g., to put a box around the minienv).
// If the environment is not mentioned in this dict, no additional options are passed.
bbox: (:),
// How to format the head of the minienv.
// If the environment is not mentioned in this dict, then it is formatted in bold.
head-style: (
proof: it => [_#{it}_],
),
// How to format the body of the minienv.
// If the environment is not mentioned in this dict, then it is formatted in italic.
transforms: (
proof: it => [#it #h(1fr) $space qed$],
)
))
```

## Coming soon / Work in progress

- Presets for multiple languages
- Separate counters
- More customization