Euler angles [incomplete]

[mcclure]

Sometime in January I needed euler angles so I threw together a quat.to_euler_angles function (and a quat.to_euler_angles_unpack function).

I would like to submit it back upstream but I think first this PR needs:

• A from_euler_angles function
• Tests
• Some kind of better documentation, for example explaining what axis standard this to_euler_angles function uses. What standard does it use ?? … I'm not sure.

[coveralls]

Coverage decreased (-0.3%) to 80.197% when pulling ae4601f on mcclure:euler-quat into ddb80f4 on excessive:master.

[mcclure]

I've been testing this in practice and I don't think it works.

Will post more about this later...

[FatalistError]

(he didn't post more about this later)

[mcclure]

I don't remember anymore what I was going to post about it later :(