[BuildStream] Buildstream releasing model

[Paul Sherwood <paul sherwood codethink co uk>]

Hi folks,
as discussed on IRC today (from [1] onwards) I (and others) think that 
the BuildStream releasing model is confusing for new users and would 
like to suggest that we change it now, rather than later.

IIUC understand it Tristan chose the current model because it is 
commonly used in GNOME projects, but I don't think that's a good 
justification.

'15:03 < paulsherwood> as a *user* I need a release the works, it should 
be obvious what that is at all times. and i need to be assured that when 
i move to the next one, the project has me covered so i don't find 
things broken in the move'

FWIW I settled on latest tag as the startpoint for new users on YBD [2], 
and the statement about which version to use is on the main page of its 
documentation, within the first screenful of the readme. I can't see why 
BST really needs anything more complicated than that, but would be 
interested to hear the reasoning.

I also chose year.week as the tag naming scheme, since that helps users 
(e.g. CI users) to immediately know how old the version of the tool is.

Note also that the current documentation doesn't actually make it clear 
which version to use (and the path most folks will follow is likely to 
lead them to master) which is a separate problem that I've raised as 
issue 528 [3]

br
Paul

[1] 
https://irclogs.baserock.org/buildstream/%23buildstream.2018-07-30.log.html#t2018-07-30T13:55:42
[2] https://gitlab.com/baserock/ybd
[3] https://gitlab.com/BuildStream/buildstream/issues/528