Merge pull request #16 from DennisOSRM/master

add <utility> to be include order agnostic
move detail tests + add initial comments (@artemp, please review)
fix typo in code comment [skip ci]
rename internal id to index, add tests
Merge pull request #18 from mapbox/type_index

Rename internal id to index, add tests
modify tests slightly to output num_iter ((3+2)-4)
boost is uneeded for unit.cpp tests
enable ctor's for valid types at compile time
[travis] multi-os
fix path to boost/variant.hpp on linux
move variant and friends into mapbox namespace for easy integration
fix namespace
inline accessors/setters
default ctor : initialise with default contructed first type in parameters pack
add default ctor test
c++11 : use type aliases instead of typedefs
converting operator=
avoid wrapped object copying
fix move ctor + housekeeping
add <string>