Merge pull request #9 from slazav/master

fix argument type warning in gtk_file_chooser_set_current_name

GUI: expand the image properly (pack bottomhbox with fill=expand=TRUE)

GUI: use correct action parameter in save_as dialog

Update README to include how to build from source.

Remove unused variables.

Add a function prototype, and remove one.

Unref G3dataApplication when closing the last window.

Add a key press event handler for the image area.

Make windows opened by Open action focused and raised to top.

Set filenames pointer to NULL initially.

Command line options affect program behavior.

Remove some unnecessary headers.

Remove dead code.

Add support for outputting error estimates.