Completeness status of musl

[Rich Felker <dalias@aerifal.cx>]

Based on nsz's work (http://port70.net/~nsz/musl/), things look pretty
good! The remaining interfaces musl is missing seem to be (broken down
into the sort of work involved):

Major new code:
- Dynamic loader (dlopen/dlsym)

Moderate-effort new code:
- POSIX Asynchronous IO
- Date parsing (strptime and getdate, etc.)
- XSI search.h functionality
- Network interface listing (if_nameindex)
- Various minor XSI legacy/junk interfaces

Importing external code, with minor cleanups:
- C99 and some XSI-extension math functions

Importing external code, with major cleanups or rewrite:
- PRNG (random)

Dummy/wrapper/trivial code:
- Old netent stuff (which will just be dummies)
- Some locale_t functions (isw*_l)
- Some CX wide string functions
- Floating point environment (fenv.h)

In addition, some existing interfaces still have missing functionality
or need rewrites to meet the desired levels of performance, robustness
against low-memory or large-input conditions, etc.

Rich