Initial CAPS IPC structural encoding and decoding support. Note that the

Initial CAPS IPC structural encoding and decoding support.  Note that the
kernel is uninvolved (other then in supplying the IPC mechanism).  After
careful consideration I decided that XML was just too much overkill but that
a human-readable format is still desireable.  The encoding format supports
integers, strings, opaque data, arrays, and is extensible and structural.

An example encoding of the struct passwd record for user 'nobody':

    Spasswd{F1D"nobody",F2D"%2a",F3Dfffe,F4Dfffe,F5D0,F6D"",F7D"Unprivileged%20user",F8D"/nonexistent",F9D"/sbin/nologin",FaD0}

Class elements include (S)tructure, (F)ield, (D)ata, (A)rray.  Data types are
free-form numeric (stored as hex), with the source responsible for encoding
negative numbers with a '-', and quoted opaque data (e.g. strings).  Any
class element may recurse using {}.  Structures and Arrays always recurse.
Unknown recursions are ignored by the decoder (for future backwards
compatibility).  Whitespace is allowed but most non-alpha-numeric characters
must be %-hex-escaped.

The decoder understands simple integer types, arrays, buffers, embedded
sub-structures, and string pointer structural elements.  It does not (yet)
understand multi-dimensional arrays, sparse element notation, or ** pointers.

This is a nice, compact encoding format that can be used for both packetized
messages and persistently-connected streams.  The initial commit only supports
full-messages, however.