* TeamCity: change test matrix and test scripts

Changes test matrix to test:

* 1.13 through 1.16 on linux/amd64
* 1.15, 1.16 on windows/amd64
* 1.15 on linux/386

Also includes tests on go-tip for windows/amd64 and linux/amd64
(currently disabled, but can be turned on in a PR).

Changes test scripts to automatically select the latest patch version
of Go.

* CI: remove Travis-CI and Appveyor configuration

* add -json flag when running tests on TeamCity

* introduce TeamCity builds

* restore gdbserial constants for 386

Otherwise compilation fails.

* skip TestAttachRequest on Windows as it never finishes

* run tests on 1.16beta1