Brotli support

[FND]

I was just curious how this compares to Brotli compression, so I added what seems like the minimum (note the full commit message) to get a rough idea. Turns out the difference is insignificant, at least with default options.

Feel free to reject this PR if it doesn't fit your needs.

Results

|  no of tickers |       json |    gzipped json |     brotli json |      proto |   gzipped proto | proto size(%) of json |    gzipped proto size(%) of gzipped json |
|         500000 |   16286210 |         4263910 |         4178919 |    6000013 |         3653864 |              0.368411 |                                 0.856928 |
|        1000000 |   32571921 |         8528041 |         8355513 |   12000013 |         7308209 |              0.368416 |                                 0.856962 |
|        5000000 |  162863911 |        42640634 |        41794496 |   60000013 |        36539648 |              0.368406 |                                 0.856921 |
|       10000000 |  325727432 |        85277921 |        83581464 |  120000013 |        73078030 |              0.368406 |                                 0.856940 |

Thanks for your write-up and this repo!