Fails to parse `--hash=` values embedded in requirements.txt

The contents of `requirements.txt` used for parsing: https://github.com/anotherbridge/pdfalyzer/blob/master/requirements.txt

Within the following code: [extractor.rs](https://github.com/aswinnnn/pyscan/blob/master/src/parser/extractor.rs#L33)

Here's the `Err` values:
```
[
found ''\\'' at 68..69,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found ''\\'' at 68..69,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found ''\\'' at 71..72,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found ''\\'' at 72..73,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found ''\\'' at 70..71,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found ''\\'' at 68..69,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found ''\\'' at 75..76,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found ''\\'' at 81..82,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found ''\\'' at 66..67,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found ''\\'' at 65..66,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found ''\\'' at 79..80,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found ''\\'' at 67..68,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found ''\\'' at 72..73,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found ''\\'' at 70..71,
]
[
found end of input at 0..1,
]
[
found end of input at 0..1,
]
[
found end of input at 0..0,
]
Ok(Dependency { name: "lxml", extras: [], spec: None, marker: None })
```

I added `lxml` at the end of the file to see if it was a file quirk, and unfortunately not. Is this because it's unsupported in pep-508 crate for now? Wouldn't parsing the text before `;` would be a feasible workaround?

Your crate is one of the core ones I use [issue originally mentioned at aswinnnn/pyscan#16] and would appreciate it if you could look into it. Thanks.