More ligatures

I really love these very unique ligatures. I also like how well they scale. The lines of the `===` lig are evenly spread on many font sizes - more than in other fonts.

But I'm missing some I'm already used to. I think Fira Code is a great example of which ligatures could be implemented. It contains quite a few. But also some got removed again because they caused trouble in some circumstances. So, the ligature list is also based on some experience.

The most important ones for me are:

- `==` `!=` (if I stumble over them in JS, or for other languages)
- `:=` (Golang)
- `?.` `??` (Very close to become part of JS)
- `|>` (pipeline operator, might come to JS too)
- `<|` (some functional languages also use this one)
- `` `` (HTML, XML)
- `` (CFML, not sure if other languages use these too)
- `+=` `-=` `*=` `/=` `++` `--` `&&` `||`
- `__` (CSS with BEM)
- `.=` (PHP)

I'm also a fan of contextual alignment, when `0xFF` looks more like `0×FF` (the x turns more into something like the `×` in HTML), or the allignment of `:` between numbers.

I hope these find their way into Inconsolata as well.