iccbeta 1.2.0: Direct icc calculations and improved error handling

Feature

• Added automatic calculation of icc on lmer model objects.

Changes

• Added improved error messaging related to presence of missing values and
  dimension mis-match.
• Added ORCiDs to DESCRIPTION
• Increased version dependencies.
• Enabled use of OpenMP and C++11.
• Added CITATION information for the R package.

Documentation

• Switched documentation to use Markdown.
• Improved contents of documentation.

Deployment

• Enable the default TMSALab Travis-CI configuration.
• Enable code coverage checks.