Discussion about axes defaults

Follow up from #665 , hopefully this can be a bit more organised :)

First: thanks for this package! I'm moving as much of my data processing to Julia as possible, and it's so convenient to make nice maps from the Julia shell.

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The default behaviour of `axes` seems to depend on the `frame` option. Example:

```julia
julia> basemap(region = (-90, -70, 0, 20), Vd = 2)
psbasemap -R-90/-70/0/20 -JX14c/0 -Baf -BWSen -P -K > /tmp/GMTjl_tmp.ps

julia> basemap(region = (-90, -70, 0, 20), frame = (annot = :auto, ticks = :auto), Vd = 2)
psbasemap -R-90/-70/0/20 -JX14c/0 -Bpaf -P -K > /tmp/GMTjl_tmp.ps
```

In the second case, there is no `-BWSen` so now all axes are annotated. With the introduction of #666 and similar aliases, we would already have e.g. `frame = :full` for doing that. So maybe `frame = (kwargs...)` where kwargs does not contain `axes` should also produce the `-BWSen` behaviour?

Start with the basemap entry point and reproduce the two frame examples from this issue, comparing the generated psbasemap commands. Read the discussion in #665 and the aliases introduced in #666 before deciding the intended default. Done means the frame keyword behavior is agreed and consistently reflected in the generated axes options.

Written by the indexing model from the issue text.