Disable travis cache

[alexheretic]

• Disable travis caching
• Remove appveyor config * readme status

Travis caching for cargo doesn't really seem to work very well. It noticeably decreases worst-case performance and a nightly project will hit the worst-case fairly often. It seems worse still on windows builds where some have been timing out in the final cache stage after succeeding.

I wondered how bad it would be without any caching.

Cache

No Cache

[alexheretic]

I also disabled incremental compilation which makes sense with the no-cache approach and should be a little faster.

[Xanewok]

Interesting - from my own experiments with Travis I noticed that caching immediate artifacts shaves off 5min of build time while downloading the cache takes no more than 2 minutes, ultimately offering a speedup. However Travis Windows runs are noticeably slower and cutting max time from 41 min (or even failing to cache) to 26 min on every run might be more beneficial in the end.

[alexheretic]

Travis caching does have a better best-case than no caching, at least on Linux. However, it has even longer worst-case build time as unpacking and packing the cache is just not very fast.

So the argument is that for nightly builds you see too much of the bad for the good to be worth it. Once you throw in the current travis-windows cache behaviour it's not just slowing us down, it's tripping us up.

[Xanewok]

Right, it makes sense to amortize the cost and land this. Thanks for looking into that!