Simpler code blocks

When looking at https://github.com/executablebooks/MyST-Parser/blob/f32bd380bdec755238566fa91352f9ed1d491036/docs/examples/wealth_dynamics_md.md, currently the code blocks are done as follows:

```{code-block} python
import numpy as np
import matplotlib.pyplot as plt
%matplotlib inline

import quantecon as qe
from numba import njit, jitclass, float64, prange
```

Would it make sense to for the following to be a shortcut for the above:

```python
import numpy as np
import matplotlib.pyplot as plt
%matplotlib inline

import quantecon as qe
from numba import njit, jitclass, float64, prange
```

As that is the common syntax to denote code blocks at GitHub / GitLab, etc.

[chrisjsewell]

another feature I’ve been long missing is side by side code blocks

FYI @certik you may also want to check out the https://sphinx-panels.readthedocs.io extension for this use case, which I’ve literally just created this week for another project 😁 (as with any sphinx directive, it can also be used in MyST)

[certik]

Btw, another feature I’ve been long missing is side by side code blocks, which you also implemented. Very exciting, I can now convert this page: https://www.fortran90.org/src/rosetta.html which was a pain to maintain in rst.