Specification compatibility improvements

[amis92]

I've notices some unchecked boxes in spec compatibility in README, and decided to give it a try.

I've fixed 3 items from the checklist:

• added octal scalar number parsing: 0o [0-7]+ (base 8 integers), finishing spec 2.19 (Integers)
• fixed empty content parsing (spec 7.2)
• added support for BOM parsing, and spec 5.1 and 5.2 examples

Additionally, I've fixed some test issues that occurred on my windows machine with Polish language, namely normalizing line-endings and locale-specific parsing.

I've wanted to finish off full spec example set, but didn't get any more time and so I'm opening the PR as-is for now.

[hadashiA]

Greate works. Thank you very much. I will merge them.

( By the way, I may fix the following two points later.

• ReplaceLineEndings is an API that is not in the .NET Standard, so unity test seems broken.
• The base 8 integers is correct as a specification, but may not be expected by many people. We may consider making it an optional behavior.

At any rate, I think it is a big improvement. Thanks.