Support toml v0.5.0

[yassun7010]

For toml v0.5.0 release, I posted a pull request for a partial support before(see #116 ).

This time, I have made complete support and tests for toml v0.5.0. Please consider it.

Change points

• [x] Add dotted keys.
• [x] Add hex, octal, and binary integer formats.
• [x] Add special float values (inf, nan)
• [x] Rename Datetime to Offset Date-Time.
• [x] Add Local Date-Time.
• [x] Add Local Date.
• [x] Add Local Time.
• [x] Allow space (instead of T) to separate date and time in Date-Time.

[emancu]

We can drop the Ruby 2.2 version and that will make travis pass. Would you mind to update .travis.yml removing that version but adding 2.6 as well?

That would be the last change and we can merge this PR and release a new version

[yassun7010]

Yes, please to add 2.6, thanks.

[emancu]

@yassun4dev I just pushed the update to .travis.yml, yo uneed to rebase on that change