nbdev_bump_version destroys literate programming in settings.ini

# Reproduction

1. Create a new nbdev repository
1. Examine the settings.ini file, which contains comments and variable substitution
1. Execute the nbdev_bump_version command
1. Observe that the settings.ini file now lacks comments, and variables have been replaced with their hardcoded values.

# Solution

Just a simple terminal command would suffice
```bash
new_version="0.1.2"
sed -i "s/^\(version[[:space:]]*=[[:space:]]*\).*$/\1 ${new_version}/" settings.ini
```
or in python
```python
import re

new_version = "0.1.2"

with open("settings.ini", "r") as file:
content = file.read()

content = re.sub(r"^(version\s*=\s*).*?$", r"\1 " + new_version, content, flags=re.MULTILINE)

with open("settings.ini", "w") as file:
file.write(content)
```