libxo-0.6.0

• Add --with-retain-size to set the size (in bits) of the retain hash buckets
• Add The Argument Modifier ({a:})
• Add retain and no-retain to --libxo
• autoconf: Add test for monitor.h
• Document quote heuristic
• go deep with nroff backslashes
• Use "ULL" for 32 bit check
• add xo_retain_clear and xo_retain_clear_all
• docs: combine two 'handles' section; move command line argument section
• handle GETTEXT when msgfmt isn't where it's supposed to be (FreeBSD)
• make 'retain' a flag (XOEF_RETAIN) instead of a role; it's simpler, and doesn't feel as tacky. "{R:}" was painful to document, which means it's painful to use.
• new xo_emit_f functions
• nuke some unused UNUSEDs
• test code: path must be static
• update test cases