Adopt New Official Extensions for ALAN3 Solution and Transcript Files

[Tristano Ajmone]

Switch to the upcoming official extensions .a3s and .a3t (see #2) for ALAN3 solution files and transcripts, respectively:

• Change file extension of all:
  • Solution files: .a3sol → .a3s
  • Transcripts: .a3log → .a3t
• Update all repo files accordingly:
  • Documentation (.md).
  • Git and EditorConfig settings files.
  • Scripts:
    • Bash .sh (none)
    • Batch .bat
    • SED scripts? (none)
• Update Wiki accordingly (not needed).