Phalcon\Security::computeHmac() plus many bug fixes

[ghost]

The initial idea of this PR was to introduce Phalcon\Security\computeHmac() function which computes HMAC of the given message — it can be used to verify both the data integrity and the authentication of a message. One of its possible applications is to verify that the cookies were not tampered with.

Bug fixes included into this PR:

• Issue [BUG] Memory corruption in zim_Phalcon_Security_hash() #1340
• Issue [BUG] Segfault in phalcon.so when using Phalcon\Forms\Element::getUserOption(). #1343
• Issue [BUG] [MEMLEAK] Memory leak in Phalcon\Debug::setCharset(), setLinesBeforeContext(), setLinesAfterContext() #1345

To properly fix #1340 (and similar bugs in the rest of the code) I have made these changes:

• PHALCON_SEPARATE_PARAM() now always separates its parameter — regardless of its refcount;
• introduced phalcon_fetch_parameters_ex() function and fetch_params_ex() macro — these ones return zval** instead of zval*. However, this allows to use SEPARATE_ZVAL() on the returned arguments without worrying about memory leaks;
• introduced convenience macros for type conversion — PHALCON_ENSURE_IS_xxx(). These ones take zval** as their argument, separate it if it is not a reference and perform type conversion. These macros are friendly to memory frames; they can work with method arguments but only if the arguments were fetched with fetch_params_ex().