[RFC] viml: impl profiling on top of uv_hrtime()

Should be better than gettimeofday() since libuv uses higher resolution
clocks on most UNIX platforms. Libuv also tries to use monotonic clocks,
kernel bugs notwithstanding.

Necessary for Windows, which doesn't have gettimeofday().

Relevant issue: #831

References for `STATIC_ASSERT`:
- http://www.pixelbeat.org/programming/gcc/static_assert.html
- http://comments.gmane.org/gmane.comp.lib.gnulib.bugs/25870
- https://github.com/gagern/gnulib/blob/master/lib/verify.h
- https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61407

**UPDATE**: Since we now have a platform abstract `uint64_t` type (`proftime_T`) instead of `LARGE_INTEGER` and `struct timeval`, I'm thinking of passing by value and perhaps even eliminating some of the one-line functions.

Ping: @justinmk @ZyX-I @equalsraf
Why you are not checking for overflow? Nobody was saying monotonic clock is going to start counting from zero. In fact documentation of `clock_gettime` is saying the exact opposite and libuv is doing nothing to compensate this fact. If there was starting point at boot time then it is more then 292 years of uptime before overflow, otherwise it is somewhere between “it will overflow next second” and “it will overflow in 293 years”.