Closes #193

* Build for Python 3.10

* Update build command

bdist_wininst was deprecated in python 3.8 (and removed in python 3.10) and bdist_msi was deprecated in python3.9

rules.Match currently has an innate race condition when using
external variables. To avoid this, use a YR_SCANNER.

Removing Travis

Seems APPVEYOR_REPO_COMMIT is not getting the commit ID properly, let's try with the branch name (it should be updated at this point)

* Release GIL when compiling rules.

The compilation is a blocking operation and can be potentially CPU
intensive. There is no reason to hold GIL.

* Lock the GIL in callback to prevent segmentation fault.

To be uniform with other callbacks and to prevent the SIGSEGV we have to
lock the GIL while we want to interact with python objects. The callback
is called from a C code releases GIL. Other callback functions use the same
locking strategy.

namespace identifier to the callback

Because the function was initializing pid as 0, when the user passed pid=0 as an argument it was indistinguishable from not pid being passed at all.

Closes https://github.com/VirusTotal/yara/issues/1480

The previous commit was still wrong.

As pointed out by Arnim Rupp (@2d4d) in #172, the fix in #175 was not complete as there's was no performance gain when the callback was not provided, which is the most common case.

This function has grown too much, so it was split in multiple functions in order to make it easier to understand.

Now the rule identifier is printed as part of the warning message, the string identifier is not descriptive enough in many cases.

* When building on macos I noticed that libcrypto was not found when using
has_function(). This is because the compiler used to compile the check program
is not being told about the library and include paths. Fix it by passing those
into the has_function() check where appropriate.

* Improve callback performance for non-matching case.

Add support for a "warnings_callback" argument to Rules.match(). If provided the
function definition needs to be:

def warnings_callback(warning_type, message)

The callback will be called with a warning type of yara.WARNING_TOO_MANY_MATCHES
and the message will be a string indicating which rule caused the warning. I
think a warning type and a message is reasonably flexible in case we introduce
other runtime warnings in the future.

If a callback is not provided we print a warning on stderr using the normal
python warning system. It's worth noting the function I'm using was introduced
in python 3.2. I can switch it to something more portable if you don't want to
pull support for 2.x yet.

While I'm here, also chase the renaming of rules_list_head and other list
variables so that it can compile with latest yara master.

When compiling YARA without Python bindings, stdbool.h is actually used
if it can be used. However Python bindings completely ignore it resulting
in YARA defining its own bool type with sizeof(bool) == sizeof(int).
However before [#1377](https://github.com/VirusTotal/yara/pull/1377), this
can result in different compilation units using different sizes of
bool type and chaos ensues.