Overhaul Quil to LaTeX circuit generation

[braised-babbage]

Description

This is an overhaul of the previous code generating LaTeX circuits. I've got an example notebook included in the the examples directory. This resolves #1023.

Checklist

• The above description motivates these changes.
• There is a unit test that covers these changes.
• All new and existing tests pass locally and on Semaphore.
• Parameters have type hints with PEP 484 syntax.
• Functions and classes have useful sphinx-style docstrings.
• (New Feature) The docs have been updated accordingly.
• (Bugfix) The associated issue is referenced above using
  auto-close keywords.
• The changelog is updated,
  including author and PR number (@username, gh-xxx).

[braised-babbage]

The previous routine was not very usable, and generated ugly stuff like:

(That's X 0; CNOT 0 1; H 1)

With the update, this renders as

Attached is an example of the usage of this (showing basic functionality, showing the use of custom settings, and showing the new PRAGMA LATEX_GATE_GROUP feature).
LaTeX Circuits.pdf

[notmgsk]

The original has a drop-shadow. I dunno if I can approve not having a drop-shadow.

[notmgsk]

Neat! Looks like there is a missing dataclasses import according to the test errors.

[karalekas]

use += to build up programs -- if its annoying to use += then we should open an issue to fix whatever your pain points are (maybe the pragma and dagger?)

[braised-babbage]

I've changed the first two examples to avoid using escape characters etc. Those are built using the gate objects, e.g. Program(X(0), CNOT(0,1), H(1)). For the last example I'm going to keep it as a big multiline string -- this is how it came to me (I generated it from the compiler), and I don't think anything would be improved by changing this.

[karalekas]

this gives me an obscure error:

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-3-6f822dbd0b9c> in <module>
      1 # extra kwargs are passed are passed straight to `IPython.display.Image`
----> 2 display(prog, width=300)

~/code/rigetti/github/pyquil/pyquil/latex/ipython.py in display(circuit, settings, **image_options)
     40         result = subprocess.call([pdflatex_path, "-output-directory", tmpdir, texfile.name])
     41         if result != 0:
---> 42             raise RuntimeError("pdflatex error")
     43 
     44         png = os.path.join(tmpdir, 'diagram.png')

RuntimeError: pdflatex error

which I see in my jupyter notebook logs is actually:

! Package tikz Error: I did not find the tikz library 'quantikz'. I looked for
files named tikzlibraryquantikz.code.tex and pgflibraryquantikz.code.tex, but n
either could be found in the current texmf trees..

[karalekas]

we should add some good documentation for installing all the requirements for this module

[braised-babbage]

Adding sphinx docs, and also adding a bit more care to the error reporting here.

[karalekas]

Also, need to update the changelog -- I think this warrants the "Announcements" section.

[karalekas]

Also -- do we have a way of aligning measurement (or any gates for that matter)? See the following example where I try to measure both qubits but everything is left justified:

[braised-babbage]

There are two open features left to implement:

• Add support for rendering RESET instructions as feedback subprograms.
• Add optional support for right-alignment of terminal MEASURE instructions (on by default).

These could be part of this PR or could be part of a separate one (I think the latter is fairly easy to implement, but am running out of time for this today).

[karalekas]

some more stuff

[karalekas]

still need to update changelog, and I think the right alignment should be done for this PR. RESET and classical feedback control can definitely be another PR

[braised-babbage]

This should be essentially good to go. I've incorporated feedback, and added support for alignment of terminal measurements e.g.

[karalekas]

this is great

been addressed