Inner approximations

[bfpc]

An initial version of inner approximations for Value functions. Currently, supports only LinearPolicyGraphs, and no belief/objective states.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 98.59649% with 4 lines in your changes missing coverage. Please review.

Project coverage is 96.60%. Comparing base (c37a4f5) to head (fe2c11f).

Files with missing lines	Patch %	Lines
src/Inner.jl	98.59%	4 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #830      +/-   ##
==========================================
+ Coverage   96.44%   96.60%   +0.15%     
==========================================
  Files          26       27       +1     
  Lines        3689     3974     +285     
==========================================
+ Hits         3558     3839     +281     
- Misses        131      135       +4     

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

:rocket: New features to boost your workflow:

• :snowflake: Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• :package: JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[odow]

I'll clean this up

[odow]

I decided just to merge this. We can make improvements in subsequent PRs