Preview 8 Release

This is the preview 8 release of dotnet/iot. Given that we are getting closer to GA, most of the changes going in to these last previews will be related to stabilizing the packages for release, so there won't be a lot of additions to APIs and instead be more focused on fixing high priority bugs in order to drive a better quality. Some of the changes included in this release include:

• Moving the versions of both of our packages (and assembly versions as well) from 0.1.0 to 1.0.0.
• Fixed performance issue with our hardware pwm driver which was opening a file handle for each operation it performed.
• Fixed temperature formula on Bmx device family binding.
• Fixed bug with our LibGpioD driver for linux where it was not recognizing requests for both rising and falling edges.
• Fixed issue with I2c and Spi connection settings that was allowing them to be mutated after creation. They are immutable now.
• Added support for several new bindings in the IoT.Device.Bindings package.
• Fixed issue with the Unix hardware Pwm implementation when not using the default chip.

Special thanks to contributors that made this release possible: (not sorted by a particular order):

• @shaggygi
• @ZhangGaoxing
• @RobinTTY
• @Ellerbach
• @Frankenslag
• @microhobby
• @krwq
• @joperezr

Packages published to NuGet.org:

• https://www.nuget.org/packages/Iot.Device.Bindings/1.0.0-prerelease.19413.1
• https://www.nuget.org/packages/System.Device.Gpio/1.0.0-prerelease.19413.1