[Feat] Allow extracting code blocks with lexers

[PrashanthaTP]

Is your proposal related to a problem?

Currently as of e970a9b / dev-0.1.0,
there is no option to extract code block if lexers are used
to specify which programming language is present in the code block

Describe the solution you'd like

(Describe your proposed solution here.)

Describe alternatives you've considered

Keeping the required blocks from the output afte dumping into a file

Additional context

It is better if we can extract the code blocks with specified programming language
which could be passed as a command line argument

Lets say
this is the content of README.md

An example with python and c code

some python code here
```python3
print("Hello World!!!")
```

and some c code
```c
#include <stdio.h>
int main(){

   return 0;
}
```

IT would be useful if we get an option to extract the code block with c or python only
in addition to the option of extracting all blocks irrespective of language

[PrashanthaTP]

olle idea 👏