Second Major Release

This represents a significant release that brings a completely modified set of internals to meet current CSVY specifications (#13, h/t Michael Chirico).

In addition, a number of additional changes have been made:

• Argument sep2 in write_csvy() has been corrected to dec.
• Fixed an unclosed connection bug. (#23)
• If reading a file data.csvy without a metadata header, and a data.[yaml|yml|json] file is present (in the same directory), that will be automatically read-in as the metadata (completes requests for #10, h/t @jonocarroll)

• Expanded test suite and fixed some small bugs in the process.
• Parse YAML header file first, then pass column classes to data.table::fread to improve performance (#9, Alexey Shiklomanov)

• Removed support for utils::read.csv() and readr::read_csv() for simplicity.
• Changed example files.
• Added option to output metadata to separate YAML or JSON file. (#10, h/t Hadley Wickham)