Release 20

[Jazzpirate]

• administrative
  • sbt version increased to 1.3.13
  • move from Travis CI to GitHub Actions
    • core language and API features
  • many improvements for diagram operators
  • parser now supports block notations, within which names are preserved
  • overhaul of parsing
  • misc. bugfixes and improvements in the build system
    • integration with sTeX
  • add a standalone localpaths build target.
  • fix spurious sms dependency cycles
    • use of MMT in FrameIT
  • almost complete refactoring to make the FrameIT MMT server less dependent on user formalizations
    • use of MMT in GLF/GLIF
  • much work on the ELPI generation code
  • various improvements for GLF/GLIF (integer support, elpi generation, ...)