Changes
* Update Python support to v3.6, 3.7 and 3.8 (140)
* Add GATTS api calls and test (138)
* Add MTU exchange test (136)
* Add printing of friendly names for error codes (133)
* Update fw version check (129)
Known issues
* The python 3.6 variant seems to be prone to segfault error when opened/closed multiple times