Alliteration aside, this should provide the final piece of the puzzle
for developers that want to get started writing a new target type.
In this way, it also seeks to complement the 'dummy' interface driver
and 'faux' NOR flash driver.

Removes hello and foo commands from top-level registration.  Instead,
the dummy interface driver and faux flash driver have been augmented
to register these commands as sub-commands.

Eliminates duplicated code in script_command and handle_unknown_command.
Fixes bug with duplicated help output generated by placeholder commands.

Factors log capture while running script commands, eliminating
duplicated code between script_command and jim_capture.  Factors
setting a command's Jim "retval" into a new helper as well.

Using these new helpers in the new unknown command handler's
fixes possible regressions caused by these bits being missing.

Remove duplicated handler code by checking the running command name.

Rewrite formatting code in C, removing last remenants of TCL help code.
Sinificantly improves the readability by using smarter indent and wrap.

The add_usage_text command uses the same C handler, which was updated
to support its new polymorphic role.  This patch updates the two script
commands that needed this support: 'find' and 'script'.

Updates httpd_start() to use register_commands() for 'readform' and
'writeform' commands.  Adds server/httpd.h to export the new signatures
for this function (and httpd_stop), which allows removing the obsoleted
declarations inside openocd.c.

Adding jim_handler field to command_registration allows removing the
register_jim helper.  All command registrations now go through the
register_command{,s}() functions.

Save stack space: use a struct.  Makes it easier to add new parameters.

Converts callback to an array of command_registration records.
Moves oocd_trace driver definition to end of file to eliminate
useless forward declaration.

Uses chaining of command_registration structures to eliminate all
target_type register_callback routines.  Exports the command_handler
registration arrays for those target types that are used by others.

Replace flash_driver callback with pointer to command_registration.
Eliminates all related routines and allows drivers to omit commands.

Replace flash_driver callback with pointer to command_registration.
Eliminates all related routines and allows drivers to omit commands.