v0.6.0

v0.6.0 (2019-09-06)

Diff since v0.5.5

Merged pull requests:

• Fix promotion tests on Julia 1.3 (#207) (nalimilan)
• Bump version to 0.6.0 (#206) (nalimilan)
• Use nonmissingtype instead of Missings.T (#205) (nalimilan)
• Silence deprecation warnings from string and escape_string (#204) (nalimilan)
• Deprecate AbstractString methods for CategoricalString (#198) (nalimilan)