Add support for including QueryString in signature

[claesjac]

This PR adds a canonicalized version of the QueryString and includes that in the signature generated.

[kaltura-hooks]

Hi @claesjac,
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[erankor]

I'm sorry, this patch does not conform to the coding standards of this module.
A few things that I'm seeing -

1. It seems to be doing more work than needed in several cases - e.g.
   a. I don't see why there's a need to copy the key/values
   b. qs + qs_len calculated multiple times instead of just once
   c. Both qs & qs_len are updated each time instead of updating only qs + using the end pos
   d. Use of ngx_array_create while ngx_array_init could have worked
2. There is no handling for allocation errors
3. There are style issues that violate nginx coding standards - e.g. 80 chars width, function opening brace in new line etc.