Add gate modifiers

[rturrado]

Add gate modifiers section to docs.
Reorganize docs.

[elenbaasc]

Thanks for the nice work!

I link the new structure, however I was struggling a bit with the fact that unitary instructions are much better known in the literature as 'gates'. So I was trying to make it a bit more clear to the reader where they could find more info on gates from the General Overview page. See if you like the suggestions, or if we can think of it some other way.

I've also adjusted/reorganized a bit the text on the gate modifiers.

[rturrado]

Thanks for the nice work!

Thanks @elenbaasc!

I link the new structure, however I was struggling a bit with the fact that unitary instructions are much better known in the literature as 'gates'. So I was trying to make it a bit more clear to the reader where they could find more info on gates from the General Overview page. See if you like the suggestions, or if we can think of it some other way.

I've also adjusted/reorganized a bit the text on the gate modifiers.

I think I've applied most of your comments, plus:

• Rename unitary instruction 'Gates' section to 'Named gates'.
• Update links to 'Gates' section to point to 'Named gates'.
• Fix link to 'Grammar sections' section.

[elenbaasc]

Great, thanks for the adjustments!

I have added some minor tweaks.

Incidentally, could you add the reset as a keyword to the table of Keywords, with its use 'Measure instruction'. This is described in ticket CQT-248, but it's such a small change that we could just do it here already.

[elenbaasc]

Some minor editing of the intro to named gates.

Good job adding the modifiers to the keywords!