Various typos & fixes

[CrashTestJava]

Working on these minor issues:

• Fixing some minor typos & punctuation issues I found
• Adding a description for the ondblclick for canvas events https://www.aseprite.org/api/dialog#dialogcanvas
• Add app.clipboard to app.md https://www.aseprite.org/api/app#app
• Add mousecursor docs to dialog.md https://www.aseprite.org/api/dialog#dialogcanvas

I'll update this with more things soon

[CrashTestJava]

@dacap can you assign me to this?

[dacap]

@CrashTestJava 👍 I'll assign this to you, I'll also add you with triage role in api and docs repos so you can assign you issues.