Added tests for unicode content and updated parser to manage utf-8

[Daniel-KM]

The parser is not unicode compliant: see the test cc412e4#diff-8b846e29de17835941c7735362aefedd
This patch fixes it.

[Daniel-KM]

There are small changes to do, but everywhere in the parser, so this is based on the last main update of the tool made by @aidantwoods.

[NightScript370]

Does this have a chance of ever getting implemented?

[hkdobrev]

✏️ length

[aidantwoods]

@NightYoshi370

Does this have a chance of ever getting implemented?

I don't see why not :)

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Couple of comments related to the changes:

Since this is based on #514, it's probably best to get that rebased on master and merged before tackling this one.

I think that in pretty much all cases getting utf-8 compatibility will just be a case of swapping the byte string functions for the mbstring ones (as this PR effectively does). This since we actually care about characters in all cases I can recall, and not bytes – bytes just happen to work for common Latin chars.

Given the discussion around #561 and related, since we already use the mbstring extension currently, we should just state that dependency (and now do). Hence we should just assume that the mbstring functions exist, and not implement our own compatibility layer. If someone really can't install mbstring then they will require an extension to implement a polyfill – they are best positioned to choose a polyfill to do this knowing their specific requirements. Alternatively (and preferably), they can just install mbstring :) (a polyfill is really only if they have no control over the PHP installation and just have to work with what they have).

[aidantwoods]

I've now resolved the merge conflicts in and merged the pre-requisite PR #514.