Fix #56
Delete empty space
Fix #8
Fix #40
Formatting
Remove extra function call
Update README.md
Fix #37
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Update README.md
Add glfwPostEmptyEvent() support.
Add glfwSetDropCallback() support.

The cgo to Go type conversion in `goDropCB` is unfinished and needs to
be improved.
Update README.md
Update README.md
Update README.md
Add mods parameter to character callback support.

Requires github.com/shurcooL/glfw on add-mods-to-char-callback branch,
currently not merged upstream.