WIP: Wavedrom cli integration

[bavovanachte]

PR for issue #23 . So far it seems to roughly work for html and pdf builds, but the conversion between svg and pdf looks messed up. Need to investigate that further.

TODO:

• [x] Investigate pdf conversion issues with cairosvg
• [x] Document the changes
• [x] Cleanup (docstrings, pylint, move wavedrompy code to its own wrapper)
• [x] More extensive tests

As this change effectively makes wavedrom-cli the default image renderer over wavedrompy, this could break existing builds. It will be released with a major version bump

[bavovanachte]

Investigate pdf conversion issues with cairosvg

I've done some checking and I've tried with different tools (svglib, cairosvg and inkscape). Overall, the rendering is ok, issues start to arise when more complex svg styling is applied, like in the json below:

{"signal": [
        {"name":"clk", "wave": "p.....PPPPp...." },
        {"name":"dat", "wave": "x....2345x.....", "data": "a b c d" },
        {"name":"req", "wave": "0....1...0....." }
],
"head": {"text":
        ["tspan",
                ["tspan", {"class":"error h1"}, "error "],
                ["tspan", {"class":"warning h2"}, "warning "],
                ["tspan", {"class":"info h3"}, "info "],
                ["tspan", {"class":"success h4"}, "success "],
                ["tspan", {"class":"muted h5"}, "muted "],
                ["tspan", {"class":"h6"}, "h6 "],
                "default ",
                ["tspan", {"fill":"pink", "font-weight":"bold", "font-style":"italic"}, "pink-bold-italic"]
        ]
},
"foot": {"text":
        ["tspan", "E=mc",
                ["tspan", {"dy":"-5"}, "2"],
                ["tspan", {"dy": "5"}, ". "],
                ["tspan", {"font-size":"25"}, "B "],
                ["tspan", {"text-decoration":"overline"},"over "],
                ["tspan", {"text-decoration":"underline"},"under "],
                ["tspan", {"baseline-shift":"sub"}, "sub "],
                ["tspan", {"baseline-shift":"super"}, "super "]
        ],"tock":-5
}
}

• cairosvg doesn't render the text well, messing up the X coordinates
• svglib just drops most of the text (or renders it outside of the canvas)
• inkscape seems to render it properly

For now, I'm going to stick with cairosvg. I really want to avoid adding inkscape as a dependency (I think @wallento had the same idea), and I doubt the lack of fancy formatting is a real issue. I'm not 100% sure the fault is with cairosvg either (don't know enough about svg to judge). If someone really needs it, I could add an "inkscape rendering mode" later on

[bavovanachte]

Added tests for wavedrompy and wavedrom-cli pdf builds separately.

[bavovanachte]

I will merge this and push a 3.0.0 alfa release to facilitate testing.