POSIX 2013 audit

Mostly manpage-shuffling according to the changes in the corrigendum,
wording changes and more idiomatic expressions.
All this is finished up by marking the POSIX 2013 conformant tools
with
.St -p1003.1-2013
which is not available in older mandoc builds or nroff, but which
reflects what we actually did, so who cares?

This is a huge step and it's not far until we can release sbase 0.1.

wc.1

@@ -1,4 +1,4 @@
-.Dd March 18, 2015
+.Dd March 27, 2015
 .Dt WC 1
 .Os sbase
 .Sh NAME
@@ -28,5 +28,5 @@ Print the number of bytes | lines | characters | words.
 The
 .Nm
 utility is compliant with the
-.St -p1003.1-2008
+.St -p1003.1-2013
 specification.