* Adds pkg/savegame to store user progress thru Level Packs.
* The savegame.json is mildly tamper resistant by including a checksum
along with the JSON body.
* The checksum combines the JSON string + an app secret (in savegame.go)
+ user specific entropy (stored in their settings.json). If the user
modifies their save file and the checksum becomes invalid the game
will not load the save file, acting like it didn't exist, resetting
all their high scores.
Updates to the Story Mode window:
* On the LevelPacks list: shows e.g. "[completed 0 of 3 levels]" showing
a user's progress thru the level pack.
* Below the levels on the Detail screen:
* Shows an indicator whether the level is completed or not.
* Shows high scores (fastest times beating the level)
* Shows a padlock icon if levels are locked and the player hasn't
reached them yet. Pops up an Alert modal if a locked level is
clicked on.
Scoring is based around your fastest time elapsed to finish the level.
* Perfect Time (gold coin): player has not died during the level.
* Best Time (silver coin): player has continued from a checkpoint.
In-game an elapsed timer is shown in the top left corner along with the
gold or silver coin indicating if your run has been Perfect.
If the user enters any Cheat Codes during gameplay they are not eligible
to win a high score, but the level will still be marked as completed.
The icon next to the in-game timer disappears when a cheat code has been
entered.
* The "Story Mode" button on the MainScene opens the levelpacks window.
* Levelpacks from all places are shown (built-in and user files), basic
level picker works.
* When playing a level out of a levelpack: the PlayScene gets the file
data from the zipfile and plays it OK.
* When a levelpack level is solved, the "Next Level" button appears on
the success modal and hitting Return will advance to the next level in
the pack. The final level doesn't show this button.
* The user can edit levelpack levels! Clicking the "Edit" button on the
Play Mode moves the loaded level over to the EditScene and the user
could save it to disk or edit/playtest it perfectly OK! The link to
the levelpack is lost upon opening in the editor, so the "Next Level"
victory button doesn't appear.
The title screen is now responsive to landscape mode. If the window is
not tall enough to show all the menu buttons (~600px) it will switch to
a horizontal layout with the title on the left and buttons on the right.
WIP "Story Mode" button that brings up a Level Packs selection window.
Adds `doodad levelpack create` and `doodad levelpack show` commands to
the CLI tool to create levelpacks.
A levelpack is a ZIP file containing a descriptive index.json and
directories for levels and doodads.
