Merge pull request #18 from Hakansv/master

Adaption to internationalism
Issue 15 related: fix computation of alpha.

Alpha (transparency in OpenGL) should not depend on how strong the radar return is.
Merge branch 'master' of https://github.com/canboat/BR24radar_pi
Refactor drawing of radar blobs.

draw_blob_gl() used to draw too big blobs close by. Because it drawed over the same pixel (after translation from
the (alpha,distance) plane to the cartesian plane that we draw onto using OpenGL the transparency seemed to be reduced.

The new code is more careful in what it draws exactly. This seems to have the desired effect:

- Transparency over the entire image is constant.
- Range seems more exact as well.

Resolves #15.
Resolves #14.
Update README.md
Improve alarm zone rendering, detection and audio.

This relates to issue #21.

- Fix the rendering of the alarm zones using the new improved draw_blob_gl().
- Fix the generation and detection of alarms.

What is still missing is a way to disable the alarm, instead of it only sounding once. I think the simplest way is to pop up a
confirmation dialog that a bogey has been detected. Until this is confirmed we should keep playing the sound.
Improve alarm zones

- Add a dialog that shows the alarm, and when the next sound will be generated. If this new dialog is confirmed or closed the alarm
  will be silent until there are no bogeys and fresh bogeys enter the alarm zone.
- Add a fallback sound -- a simple bell sound (wxBell()).
- Render the zone relative to the boat, not north. Still to check whether the alarm zones actually match properly with the rendered
  zone.
Small cosmetics
Merge branch 'master' of https://github.com/canboat/BR24radar_pi
Merge pull request #1 from canboat/master

40429