SVG logging

[wjcarpenter]

I wanted to make some screenshots of some things I was doing with this graphics package,
so I implemented a way to get SVG output. If you find it interesting, feel free to add it
to the library (or any similar driver libraries you have).

SVG logging sends equivalent SVG directives to the ESP log (usually uart0).
It logs at the logging level and with the logging tag specified. That
should make it straightforward to use text tools to carve the actual SVG
out of the log. There is an optional "cut line" argument to the lcdSvgLoggingEnd.
If provided, it is logged as-is and could be used to automatically separate
multiple chunks from the overall output.

There is no inherent overall background color. If you want one, you
should start with lcdFillScreen() within the SVG logging.

SVG output can be quite verbose (especially for things like text that are
drawn a pixel at a time). It also slows things down a huge amount. In fact,
it makes things so slow that there are task delays of 1 tick sprinkled
throughout to avoid tripping the task watchdog timer.

[nopnop2002]

Thank you for your PR.

I don't know anything about SVG, so it will take some time to understand this.

[wjcarpenter]

In issue #31, I attached a ZIP of the SVGs for the library's sample app so you can get an idea of what the output looks like. You can also see some examples of my screens here: https://hackaday.io/project/184926-blexmang/log/205726-user-interface-elements (Because I am using a TTGO T-Display in landscape mode, and because that web site doesn't accept graphics as SVGs, I used some common tools to convert them to PNG and rotate them. But they are otherwise identical to the SVGs.)

[nopnop2002]

Thank you.

I don't understand SVG yet