Support new keywords

[Phyks]

It would be great to be able to support new keywords.

Among them, I can see:

• \hbar
• \dagger
• transposition of a matrix
• \left| x \right> for kets in quantum mechanics. Conversely, \left< x \right| for bras.

[zamicol]

I've been using ℏ for now for hbar.