AT_v0.20 is on github now, https://github.com/espressif/esp8266_at
You can report bugs in "Issues", or fix bugs by "Pull Requests" there.
1. Here are two branch of esp8266_at:
branch “master” is the source code which will be official released after test，
branch “developing” is the source code in developing.
Please submit your code on branch “developing” , and we will merge it to branch “master” if test pass.
2. In folder "bin",
sub-folder "newest" keeps the latest bin which just be generated,
sub-folder "v0.20" keeps the official released bin of version 0.20.
3. More information on wiki https://github.com/espressif/esp8266_at/wiki
Thanks for your interest in ESP8266!