[tlbuild] tl19 schedule and cweb(bin)

[Karl Berry]

Hi - for TL 2019, I'm hoping for close to the same schedule as last
year. Posted at tug.org/texlive, and copied here for convenience:

22feb: sources committed, builds begin.
 1mar: tlnet (and TL'18) frozen, tlpretest starts, CTAN updates continue there.
22mar: code freeze for final build, major bug fixes only.
 5apr: final updates from CTAN, final doc tweaks.
12apr: deliver TL image for TeX Collection packaging/testing.
19apr: deliver TeX Collection DVD image for manufacturing.
30apr: public release (also of MacTeX).

If you built the binaries distributed for some platform in the past, and
won't be able to do so this year, please let me know.

On the code front:
- Jonathan has committed a new version of XeTeX (with all the
various changes we have been accumulating),
- Luigi has committed the new version of LuaTeX, and
- I have committed (r49626) Andreas Scherer's
CWEBbin for the new cweb (https://github.com/ascherer/cwebbin). It has
support for translations and plenty more. It is probably necessary to do
a complete build and not just make in the web2c build dir after this,
due to unresolved problems in the Makefiles (dating back to when cweb
was first introduced into TL).

So, it'd be fine to try a test build now, also fine to keep waiting :).
I hope to get the latest ICU into the source tree this week.

Thanks,
Karl