Changes to version 1.2.0
- add S3 methods
  - `matrix` class data is automatically converted to `data.frame` class
  - return tibble class when data is tibble
- fix several bugs
  - return rownames of input data

Changes to version 1.1.2

- fix several bugs
  - the column names are inappropriate.
  - the columns are droped when they contain only one level.

Changes to version 1.1.1

- Pull Request #1
  "add column name when when columns has binary value"
  (https://github.com/toshi-ara/makedummies/pull/1)
  Thanks to Kohki YAMAGIWA for the contribution.

Changes to version 1.1

- makedummies() accepts a tbl class data.
- fixed bug when "POSIXt" class is included.
