Add support for PHP

[jvoisin]

This commit was inspired (but completely rewritten) by https://blog.jmpesp.org/2020/01/fuzzing-php-with-domato.html

The php_generated.txt file was generated via parse_types.py

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[jvoisin]

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[ifratric]

Thanks, looks cool!

A couple of notes:

1. Callbacks are currently unused (<fuzzfunction> always point to phpinfo). Generating callback code in a similar manner to the main function could potentially expose additional bugs, especially if callbacks get access to the same variables / can mess up stuff that the caller didn't expect.

2. Currently, the return vallues from the function / method calls are ignored. In cases where function / method calls return non-trivial types, wouldn't it be better to store these return values in variables and use them as function arguments in later calls or potentially call methods on these "generated" objects?

[jvoisin]

I wanted to keep the pull-request simple. I added your suggestions (and the other items on my todo-list) in the README.md file.

[ifratric]

Alright, merging as is for now. Thanks!