Added a link to the OSv libc (based on musl).
Renamed the minimal example program as per its proper scope.
Implemented the classic "Hello, world!" example program.
Added some miscellaneous to-do items of note.
Implemented the <errno.h> header per the C11 standard.

However, thread-local storage isn't supported yet, so 'errno'
is at present simply a process-global variable.
Added trivial test cases for EXIT_FAILURE and EXIT_SUCCESS.
Stubbed the <stdio.h> puts() function and defined the EOF macro.
Defined the __sys_write() operation.
Implemented the __sys_write() operation for Darwin (x86-64).
Defined the system call interface explicitly in its own header file.
Implemented the <stdio.h> puts() function.
Implemented platform support stubs for bare-metal targets.
Implemented the __sys_write() operation for Linux (x86-64).
Added README notes on configuring the build for bare metal.
Added a table of other libc implementations to the README.
Renamed Ohloh to Open Hub, and removed the defunct Freecode link.