Disable AppVeyor (Windows) builds

[thk123]

A recent change stopped this branch working on AppVeyor due to the use of signal: More details in this comment: #1004 (comment)

This PR disables AppVeyor from running by deleting the yml file. I also updated the README to not include the unnecessary build icon (and corrected the branch for the travis logo.

This PR is awaiting test-gen to be brought up to speed with test-gen-support.

[reuk]

The change looks good, and this seems sensible if we're happy to completely drop windows support.

[thk123]

Do not merge - @smowton to #ifdefout the feature that doesn't compile

[pkesseli]

signal is only necessary to enable the CBMC-based test object creation strategy, correct? Can't you just add an #ifdef _WIN32 and throw an exception if somebody uses that strategy under Windows? Or perhaps even just run it without time limit in Windows and show a warning? It seems a bit overkill to drop the entire Windows support, when the product will still work fine, e.g. with the heuristic method or reflection.

At some point in the future, we can then figure out how to add support for this under Windows in the else branch.

@forejtv

[peterschrammel]

@thk123, this seems obsolete now? Close?

[thk123]

@peterschrammel yup