Add Travis-CI configuration to build the project automatically

[seporaitis]

Description

Add a simple continuous integration suite on Travis CI that verifies that the code compiles successfully using clang and gcc - both of which are most commonly used C compilers. It does not test the app itself as I haven't yet come up with an idea of how to unit test ncurses apps.

Motivation and Context

Having a continuous integration setup is a basic good practice - it will show if there are any immediate problems with the code without requiring human intervention.

How Has This Been Tested?

Ran a successful build here.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
  • [ ] I have updated the documentation accordingly.
• [ ] I have updated HISTORY document.
  • [ ] I have referenced pull request and/or issue next to the change.
• [x] I have read the CONTRIBUTING document.
• [x] All new and existing tests passed.
  • [ ] I have added tests to cover my changes.