197 pattern history

[musicin3d]

For the feature request: https://github.com/luin/medis/issues/197

This remembers the latest 5 patterns that were not already saved.

When the user types in a pattern and hits the Return key the pattern is added to the top of the list of suggestions. When a pattern is reused it is moved to the top of the list. When a sixth pattern is used, the oldest one is removed.

If the user enters a new pattern and they have saved patterns, section headers are added to the list to visually separate saved patterns from recently used ones.