Change LyX release numbering to Semantic Versioning

[Pavel Sanda]

On Mon, Jan 11, 2021 at 08:59:55PM +0000, José Abílio Matos wrote:
> Since we our release schedule is every two years this will keep us in low 
> numbers for a long time.
> 
> What do you think?

Not surprisingly, I'd propose to stay where we are.

The reasons are two:

- I prefer to stay with single digits as long as possible because it's
  easier to remember/communicate them. The moment the version numbers
  go beyond 10, you tend to lose track of versions (experience with
  firefox-like scheme). 
  
- People are already used to certain numbering scheme x.y.z where staying
  with y means fileformat is fixed. I don't see that we are really solving
  any problem with new proposal while forcing people to adopt new policies.


Major bump 2.x->3.x is fine either when we reach high x number or when
something unusual happens (e.g. XML transition, switch from Qt back to
xforms, 30 years of LyX etc. :))

Pavel