Update README.md with some up-to-date  information
Remove unnecessary gswe_planet_data_unref() calls

This introduced an ugly bug when changing from the Edit tab to Chart view
for the second time.
Add .a files to .gitignore
Move ag_window_redraw_chart() to a more appropriate place
Change deprecated GTK stock items to actual values
Add message dialogs to indicate save errors
Set southern latitude/western longitude if saved chart has negative values

Fix #16