Future EAPI/Version syntax changes

Reordering to PACKAGE OP VERSION
Replace the current:

[ ]  [- ] [: ] ... ^^^^^^^^^^^^          ^^^^^^^^^^^^

with:

 [: ] [ ] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

e.g.:

Advantages:
 * more readable,
 * easier to edit,
 * easier to validate,
 * easier to split package name from version,
 * better ground for version ranges,
 * in the future, this will allow us to dump restriction on package names not being confusing with versions.