release MeTA v1.2

New features:

• demo application for CRF-based POS tagging
• nearest_centroid classifier
• basic statistics library for representing relevant probability distributions
• sparse_vector utility class

Enhancements:

• ngram_pos_analyzer now uses the CRF internally (issue #46)
• knn classifier now supports weighted knn
• classifier cross validation can now optionally create even class splits
• filesystem::copy_file() no longer hangs without progress reporting with
  large files
• CMake build system now includes INTERFACE targets (better inclusion as
  subproject in external projects)
• MeTA can now (optionally) be built with C++14 support

Bug fixes:

• language_model_ranker scoring function corrected (issue #50)
• naive_bayes classifier scoring corrected
• several incorrect instances of numeric_limits::min() replaced with
  numeric_limits::lowest()
• compilation fixed with versions of ICU < 4.4