Add option to set custom section delimiter

[ext]

What / Why

Adds an option to set or disable delimiter used when splitting sections into nested objets.

While splitting sections can be useful in some cases it also prevents others such as sections with URLs or paths:

[http://example.net]
...

[myfile.txt]
...

While it is possible to escape the dots using myfile\.txt for this parser it may break other libraries, e.g. when the ini-file is used written/read by some other tool. In my case I receive the ini-file from an integration and have no control over it.

It PR allows setting a custom delimiter or to disable splitting entirely (for reading, writing still requires a delimiter).

References

• Fixes Section headers with '.' in them are split #60

[wraithgar]

This seems wrong.

[wraithgar]

Cleaning up old PRs and came to this one. Rebased and cleaned it up after landing #200.

However this brings up more questions such as, "should the decoded object have dot separated sections still?" This PR seems to suggest that but that seems counterintuitive.

If the problem being solved is that dots in sections don't work, this appears to be something that is feasible now:

> ini.encode(ini.decode('[http:example\\.net]\ndots=true'))
'[http:example\\.net]\ndots=true\n'
> ini.decode('[http:example\\.net]\ndots=true')
[Object: null prototype] {
  'http:example.net': [Object: null prototype] { dots: true }
}

The question to answer before a PR like this can be made is "is the delimiter kept in the decoded object?" A note on the test where this comes up has been added.