simplify tk dep too

Linux: use system tclsh
Windows: use vendored tclkit.exe
WIP: simplify lua dependency

On Windows, vendor a non-interactive lua executable (wlua). This is
important because wlua.exe doesn't steal focus like lua.exe.

On Linux, assume lua and djot.lua are available from $PATH.

Thus we skip all of that luastatic mess.
windows: make sure djotbin.exe doesn't steal focus

Hinted by the fact that LuaBinaries' wlua54.exe didn't steal focus while
lua54.exe did. The only difference was that wlua was compiled with a
`-subsystem:windows` linker option. That translates to
`-Wl,-subsystem,windows` in luastatic args.
neocities: redirect to Publish if creds are legit
make djot docs open in new tab
update new post slug hint too
delete post
consistent page title margin, simpler post list
edit post: highlight when inserting attachment
edit-post: scope functions into their blocks
edit-post: avoid calling /djot-to-html/ on startup
less eager live reload

Still perfectly acceptable I think.
fix chrome blocking exit prompt
make sure to not lose highlight when Back

TODO: Chrome doesn't allow calling a dialog during onbeforeunload:

No wonder why nobody wants to use "standard browser features" anymore.
I'm beginning to sympathize with custom-everything SPAs...
simplify & make success messages consistent

Since we now have better visual cues on submit, there's no need for the
old length "done X at Y" messages.
manage attachment: better filename error msg
fix slug/filename regex

Was invalid in browser.
edit post: highlight & warn about unsaved changes