Drop Julia 0.6 and heavy refactoring

• Use compact element printing (#195)
• Overhaul printing of types (#194)
• Improve parse constructor exception message (#193)
• Address corner cases in next_transition_instant (#192)
• Officially support Julia 1.1 (#191)
• Default to using 2019a tzdata (#190)
• Documentation update (#189)
• Fix for 32-bit "uU" dateformat issue (#188)
• Avoid using a redirecting URL (#181)
• Add Project.toml (#176)
• Define broadcastable for scalars (#177)
• Support legacy time zones (#174)
• Separate types into multiple files (#173)
• Introduce TZSource for managing tzdata source files (#172)
• Refactor Rule/Zone parsing (#171)
• Use immutable String instead of Symbol (#168)
• Drop Julia 0.6 (#167)
• Minor refactoring (#166)