Travis CI build

[AdySan]

I've attempted to enable a Travis CI build on this repo. This is the first time I've setup Travis CI, so kindly excuse any noob mistakes on my part. The build seems to be working fine, however, I have some open questions.

• This line calling ./gen_misc.sh exits with error code 0 even if the script fails. This makes the CI build rather useless. I suppose this is due to the hardcoded y I'm putting as input to the script. Is there a better way to do this?

• I've used install_toolchain.sh from esp-open-rtos, what is the best way to cite this?

• I've not sure how long Travis CI maintains the cache, but if the builds are far apart, it probably needs to build the whole toolchain, which takes about ~10mins.