fix for if png fails to download from rainviewer

ptl tool fixed, now works correctly regardless of rotation settings

Update README.md

Merge pull request ronyan#9 from ronyan/fp-track

fixed logic for 7500/7600

Merge pull request ronyan#6 from ronyan/alt-filter

tag drawing, prelim free text

preparing for free-text, bug fix for squawk stdby

magenta primary targets added; altitude filter defaults to on

Merge pull request ronyan#2 from ronyan/develop

unicode changes

Update README.md

commented out asr data saving for now, to be implemented in a later v…

…ersion