v2 API

[brentyi]

• Improved vectorization!
• Much simpler API!
• Support parallel solves over graphs with different sparsity structures!
• Dynamic graph changes without needing to re-JIT!
• Significantly less code!

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.86%. Comparing base (a544003) to head (3093119).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #16 +/- ## ======================================= Coverage 93.86% 93.86% ======================================= Files 30 30 Lines 978 978 ======================================= Hits 918 918 Misses 60 60 ``` | [Flag](https://app.codecov.io/gh/brentyi/jaxfg/pull/16/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brent+Yi) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/brentyi/jaxfg/pull/16/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brent+Yi) | `93.86% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brent+Yi#carryforward-flags-in-the-pull-request-comment) to find out more.

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