Now the script supports more flashing methods:
- JLink (with tockloader)
- OpenOCD (with tockloader)
- pyOCD
- Nordic DFU
- none (will produce an IntelHex file)

Also merged the contributions from:
- Yihui Xiong to support the Makerdiary USB dongle board
- Dennis Geurts to support Nordic DFU

Doc updated accordingly.

Imported 2 patches for Tock kernel:
- 06-add-set_vector_table_offset.patch (upstream tock/tock#1579)
- 07-nrf52-bootloader.patch (upstream tock/tock#1681)

`ioreg -P USB` doesn't work, it should be `ioreg -p USB` to get usb list in Mac OS X.

Updated the shell script that generates the certificates and the
documentation accordingly.
Caveat: now installation is a 2-step procedure, installing OS and
application are split into 2 commands.

Fixes #25

Fixed the link for TC2050 Tag-Connect programming cable. The right cable that connect to the Tag-Connect TC2050 ARM2010 adapter is the TC2050-IDC-NL instead of TC2050-IDC-NL-050-ALL.