When you mark free standing functions as `static inline` instead
of just `inline` they can not get merged across TUs and therefore
produce code bloat which is bad for the binaries size, the CPUs
instruction cache, and so on.
Please also see the discussion at:
- https://groups.google.com/forum/#!topic/mozilla.dev.platform/Ulw9HoZbSyQ
- http://stackoverflow.com/a/12836392
Note that non-fully specialized templates (i.e. with a kind of at
least `Template :: * -> *`) are `inline` by default.
