Add continuous scrolling to line cursor mode

Add continuous scrolling to line cursor mode

Do not move cursor if more lines do not exist (yet)

Revert "Do not move cursor if more lines do not exist (yet)"

This reverts commit 7539274f31c819f7227abd063883768d02f0615a.

Does not allow you to scroll to end of message.
Add config option for continuous scroll behavior

Add config option for continuous scroll behavior

Add continuous scroll option to default config
Do not move screen if we are at the bottom. Match top and bottom ranges
continuos_scroll: swap ifing order
continuous scrolling: history
t_v_m: dont escape filename when saving attachments

Extra Shellwords.escaping was introduced in 3106f6d where in reality
only functionality for saving with default filenames should be added.

The Shellwords escaping is removed. The filename is not used in any
command, and any program or command out-of-sup needs to account for
correct filename. The filename may potentially contain shell commands,
the file will be saved with the filename indicated by the SENDER of the
email.

Fixes #277.
move SupSingleton to Redwood::Singleton
Merge #279: Rename SupSingleton to Redwood::Singleton

Replaces #275 and undoes #271 in favor of a Singleton class inside the
Redwood module.
Merge branch 'develop' into maildir-root