add TinyFPGA BX support

[tinyfpga]

Add basic support for TinyFPGA BX. I would love some help to test this, I had a hard time with the B2 building a local APIO and local IceStudio and have them both work together.

[Jesus89]

Thanks! 🎉

In order to use your local Apio you need to set here the proper range (0.4.0, 0.5.0)

Then you have three options:

• Add here your external Apio binary
• OR Export your Apio binary path in the env var ICESTUDIO_APIO
• OR Activate the Icestudio virtualenv ('source ./icestudio/venv/bin/activate) and then install Apio from that session.

And this should be enough. Then run npm start to launch Icestudio.

[tinyfpga]

Hey guys, anything we need to do here to get this merged in? Can we make a beta release with TinyFPGA BX support?