Add new API chewing_version() to return runtime library version:

[kanru]

Is your feature request related to a problem? Please describe.

libchewing maintains ABI compatibility between versions. We need this new API so that wrappers can query the latest linked version (vs. compiled with version).

Describe the solution you'd like

A new API char* chewing_version() that returns string encoded version string.

Optionally

• int chewing_version_major()
• int chewing_version_minor()
• int chewing_version_patch()
• char* chewing_version_extra()

Additional context

It's nice to have to be able to show runtime version information in ibus-chewing's about page.