Add PostMultipart().
Use browser.PostMultipart() when form.enctype == "multipart/form-data"
Merge pull request #2 from haruyama/multipart

Add multipart/form-data support.
Updated the change log
Updated the readme
Updated the change log
Merge branch 'master' into checked_and_option
Add Form.InputSlice() and Form.CheckBox().

Both have same behavior.