Don't use zend_string for registerExtension- It may be freed

[TysonAndre]

... before module shutdown
(In NTS builds of PHP 7 (e.g. 7.0.9) only)

Fixes #247

This no longer returns getExtensions() in the order in which they were
registered. vector<pair<char*, v8js_extension*>>> could be added to reproduce the old behavior if this was desirable.

This is slightly wasteful of memory - A custom hash function and
equality function for const char* is possible to add to this for an unordered_map

[stesie]

Hi,

sorry for not answering on your issue earlier, and thanks for now taking care of it. Actually I started investigating yesterday night and noticed that it was related to interned strings - which aren't really duplicated by:

    jsext->name = zend_string_dup(name, 1);
    jsext->source = zend_string_dup(source, 1);

... hence zend_string_release in v8js_jsext_free_storage frees them (and hence the "use after free" error). So a different solution would have been to just test jsext->name and jsext->source to be interned and not free them then.

From a first glance at your patch it looks good to me - so I haven't tried it out yet. There are two "TODO" marks left in there, do you intend to continue on them?

Generally I'm fine with the change to an unordered map of extensions, and also to now use null-byte-terminated strings (I wouldn't expect anyone to have null-bytes in extension names) ...

[TysonAndre]

oh, you seem to be right about interned strings being freed earlier.

Misread what you said the first time, see #255 (Converts interned strings to non-interned strings)