encode html entitites

[jcpsantiago]

Fixes #10

Does not add new dependencies and tests are green.

[jnolis]

I have a question on this one. Is the list of symbols you have to encode sufficient? I think in theory there are more than that--I remember dealing with this problem before and using the textutils package for it (see here). That said, I like that your code doesn't have any dependencies so if that means we don't get every possible symbol that's probably fine. If you could just think about it that would be great!

[jcpsantiago]

I tried textutils first during debugging and used it to encode every symbol. JMeter actually complained when I encoded everything 🤷

In #10 I posted the results of pasting every symbol on my ANSI keyboard and JMeter doesn't seem to care about all of them, only the ones I encoded. Maybe it's an XML thing? I don't know :D

Sorry TL;DR: I chose these encodings based on what JMeter does, so it should be safe.