Bigger additions:

• Plugin support! That's right,
• Outline view! Makes it far more manageable to work with huge scripts/objects
• Split view! Show a linked version of one of the tabs on the right for quick editing/reference (right-click on code > Show aside)
• You can now manage GMS2 objects and shaders from GMEdit, as well as reordering/regrouping (but not creating/deleting) most other resources

Smaller additions:

• Opening an image from included files now shows it inside GMEdit
• GMEdit now supports basic INI and Markdown highlighting
  Markdown supports GML highlighting inside ```gml ...``` blocks, making it more convenient to write documentation for GM extensions right inside the project editor.
• You can now see/edit general properties of GMS2 objects in a special "properties" event
• GMEdit can now auto-detect whether to use spaces or tabs on per-file basis
• There is now a command palette (Ctrl+Shift+T or Ctrl+T,>) for accessing semi-common features and plugin commands
• You can now edit "notes" in GMS2 projects.
• You can now sort resources in GMS2 projects (via right-click menu).

Improvements:

• You can "view API" for GMS1 extensions as well
• Opening a non-project file now consistently shows a file tab and a recent project list on the side
• Code highlighting inside gml_pragma now works better.
• If a script has no JSDoc, GMEdit will guess basic argument info from code.

Fixes:

• Fixed an occasional little seam on tab UI
• Fixed "/*" in search results breaking highlighting for the subsequent matches
• Fixed GMEdit using / in new script paths while GMS2 prefers \ (causing GMS2 to later update them)
• Fixed status bar showing wrong active argument for code with 2d array accessors among arguments
• Fixed GMLive.gml icons flipping on/off when re-saving the same file with limited changes.

Notes:

Due to time constraints, and GMS1 being formally sunset 7 months ago, for future features I will no longer do GMS1 versions if that means effectively doubling the amount of time it would take to implement them. Should you find yourself in possession of free time, you are welcome to backport GMS2-specific features to work GMS1 and submit a pull request. Existing functionality will continue to work as usual.