[PATCH] log format tokens upgrade

This updates the format parser and storage objects in the Format::
namespace and separates some into separate files for SourceLayout
project dependency reductions.

Functionally it adds a registration API so components can register
themselves an array of tokens in a namespace. Registering the arbitrary
namespace "example" with some tokens ("a","b") will cause the parser to
accept those tokens in a logging format like so: "%example::a %example::b".

Due to time limitations resolving the library-library symbol
perculiarities in GCC I have had to cut short of moving the "adapt::"
and "icap::" tokens into their libraries. But have gone so far as to
make them use the registration process in this patch ready for that step.

Future work:
  - convert the error pages to use format for the page body macros
  - convert the %ssl_* tokens in src/ssl/* to use format and the
namespace "ssl::"
  - convert external_acl_type to use formats for its helper input string.

Amos