Unify interface of import function

[klmr]

There should only be one single import function that, depending on the format of the import path (and potentially other options) decides what to import from where.

One possible idea would look as follows:

• Module (qualified name — unqualified names are no longer supported):

  m = mod::import(qualified/modname)
  n = mod::import(./modname)
  o = mod::import(../modname)
  …

• Package:

  p = mod::import(pkgname)

• Module from external source:

  m = mod::import(github:qualified/modname)

  This would require the existence of a “provider” service github that knows how to locate, load (and cache?) modules from that source. This last point might become complicated once versioning is involved.

This might also incorporate version specifiers (e.g. by adding a suffix of the form >='1.0.0', or @'rev'). See #28.

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Yes, these are all unquoted. stringly typing is verboten. I’m as yet undecided whether the final version will support quoted specifications at all — probably not. Similarly, I’m not sure yet whether tidyeval support is desirable, but import_ will probably die.

[klmr]

Also consider changing the import name. I like it, but maybe alternatives are better:

• use
• lib
• load
• require

[mschubert]

superseded by #129