Enable Travis-CI

[calebepb]

Enable Travis-CI with ATA_TYPE (?) to compile and run:

• auto
• avx128
• avx256 - is it possible?
• avx512 (?)

[mvrozanti]

ATA_TYPE was renamed to REGISTER_WIDTH in 1147b8a

AVX256 build on Travis-CI was possible by increasing compiler version to g++-7 in 3712afe, but still haven't set up test scripts for the builds.

Currently allowed build failures are osx and windows platforms.

I found an issue on a not-so-unrelated repository about using Intel's SDE to test builds on a variety of architectures, including skylake. Not sure how long it would take to setup though.

I also found a repository that aims to provide a silent installer for icc/icpc compilers on Travis-CI.

[calebepb]

I think we should not use icc/icpc to compile/test your solution. The best way to use them is only showing some performance evaluation on README.MD in some in-house server

[calebepb]

Why not use SIMD_WIDTH ?

[mvrozanti]

Renamed REGISTER_WIDTH to SIMD_WIDTH in 14c7250