Add multithreaded hashing functions

[lnjX]

• QXmppError: Add fromIoDevice()
• Add multithreaded hashing functions

PR check list:

• [ ] Document your code
• [ ] Add \since QXmpp 1.X, QXMPP_EXPORT
• [ ] Fix doxygen warnings (see log when building with -DBUILD_DOCUMENTATION=ON)
• [ ] Update doc/doap.xml
• [ ] Add unit tests
• [ ] Format the code: Run clang-format -i src/<edited-file(s)> tests/<edited-file(s)>

[codecov[bot]]

Codecov Report

Merging #464 (14695e3) into master (d858e4a) will decrease coverage by 0.28%. The diff coverage is 40.75%.

:exclamation: Current head 14695e3 differs from pull request most recent head 2091300. Consider uploading reports for the commit 2091300 to get more accurate results

@@            Coverage Diff             @@
##           master     #464      +/-   ##
==========================================
- Coverage   68.70%   68.42%   -0.29%     
==========================================
  Files         277      279       +2     
  Lines       24013    24306     +293     
==========================================
+ Hits        16499    16631     +132     
- Misses       7514     7675     +161     

Impacted Files	Coverage Δ
src/base/QXmppError.cpp	0.00% <0.00%> (ø)
src/base/QXmppError.h	0.00% <ø> (ø)
tests/util.h	98.03% <ø> (+11.76%)	:arrow_up:
src/base/QXmppHashing.cpp	31.55% <31.55%> (ø)
src/base/QXmppHashing_p.h	50.00% <50.00%> (ø)
tests/qxmpputils/tst_qxmpputils.cpp	100.00% <100.00%> (ø)
tests/qxmppomemodata/tst_qxmppomemodata.cpp	98.25% <0.00%> (+<0.01%)	:arrow_up:
src/base/QXmppHash.cpp	40.00% <0.00%> (+6.31%)	:arrow_up:

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