[feature request] preview inside nvim buffer

hey. great plugin.

i was wondering if it is possible to have preview `inside a vim buffer` as a tab vertically splitted rendering all that markdown from your file, everything inside vim/nvim. I dont want always to have my browser splitted in order to write markdown and see the real time result. I just want everything inside vim/nvim.

and another feature request (if possible, ofc):

add an option to change the `syntax highlighting` for a `code` block such as:
```
```python
for i in range(100):
print("this is a statement")
```
honestly. i tried both `dark` and `light` theme and i dont really like the colors. I just want to change the colors for blocks of code in the markown. overall theme is good, but sometimes in the block code of shell there are `no colors` which is interesting because in the vim version of this plugin there is syntax highlighting for shell.

hope you are going to take into consideration. thanks.