update readme with RTKLIB info

Merge pull request #245 from semuconsulting/RC-1.6.6

update nmea GGA handler Fixes #244

Merge pull request #243 from semuconsulting/RC-1.6.5

update screenshots

update config panel

update config panels

update app image

Merge pull request #242 from semuconsulting/RC-1.6.4

update caster RTCM outputs

Merge branch 'master' into RC-1.6.4

fix & enhance base station configuration

update debian install script

update docs

update docs