bump to 1.91.4

Merge branch 'master' of https://github.com/JuliaPy/PyCall.jl

Bump to 1.91.2 (JuliaPy#678)

avoid jl_value_ptr (JuliaPy#671)

* avoid jl_value_ptr

* use pointer_from_objref to avoid rooting requirement for unsafe_convert

various fixes to array conversions (JuliaPy#668)

* 0-dimensional PyArray

* gc safety and CartesianIndex support in PyArray

* PyArray bounds checking

* rm redundant methods

* another simplification

* no sum for empty tuples

* fix docstring

* consolidation of Array{PyObject} conversion, add a missing GC root, pysequence check fix

Add PySide2 support to pygui (JuliaPy#649)

* Add PySide2 support to pygui

* change pyside2 to :qt5 and add :qt_pyside2

* refactor codes

Use find_libpython.py in deps/build.jl (JuliaPy#556)

* Copy find_libpython.py from PyJulia

* Call find_libpython.py from deps/build.jl

* Handle the case find_libpython.py cannot find libpython

* Store full path to libpython in deps.jl

* Update find_libpython.py

* Use --candidate-names in the fallback path

* Improve debugging message

* Use pythonenv in when invoking find_libpython.py

* Add _linked_libpython_windows

Don't steal reference from existing Python object (JuliaPy#553)

* Don't steal reference from existing Python object

closes JuliaPy#551

* Refactoring: add pyreturn function

* Fix pystealref! in pyjlwrap_getattr

* Fix pystealref! in pyjlwrap_iternext

Segfault with Python 3.7 (JuliaPy#540)

* Use correct Python version in x64 AppVeyor

* Test with Python 3.7 in AppVeyor

* Implement PyDateTime_CAPI change in bpo-10381

simplify pycall! code to eliminate argument-tuple caching … the logic…

… was just way too complicated and hard to get right, for questionable gain