Support measurable frequency to 1.5 GHz

1. support measurable frequency to 1.5 GHz, default setting 1 GHz, accurate measurement up to 1.35GHz.
2. fix: unexpected 0.3dB offset of s21 in thru
3. fix: mark all off bug
4. fix: clutter display when standing wave ratio is infinite
5. add version & info command
6. add REAL IMAG R X trace format

more details :
http://deepelec.com/2019/12/30/nanovna-f-0_0_5/