#550 update tcl tutorial to cover all commands

[Larry W. Virden]

It would be really useful if there were a way to search the tutorial to find the pages which discuss a particular command. Also, browsing the pages, these commands didn't seem to be discussed much if at all:

after, append, apply, auto_execok, auto_import, auto_load, auto_mkindex, auto_qualify, auto_reset
bgerror, binary, break
chan, class, copy,
dde, define
encoding, exit, expr,
fcopy, filename,
history, http,
if, incr,
join,
lassign, library, load, lrepeat, lreverse
memory, msgcat, my
next, object
parray, pkg::create, prefix,
refchan, registry, rename, resource,
safe, scan, self,
tcl_endOfWord, tcltest, throw, transchan, try,
unknown, unload, unset, update, uplevel,
variable, zlib,