added EC5 clamp flag

[zycyc]

note that hip.go must use EC5Clamp=true to prevent not having a target layer, but this is a useful flag for models like eboa to let EC5 have free flow plus-phase pattern

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: -0.02% :warning:

Comparison is base (7b6400f) 28.65% compared to head (a97f8fd) 28.64%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #315 +/- ## ========================================== - Coverage 28.65% 28.64% -0.02% ========================================== Files 89 89 Lines 15897 15903 +6 ========================================== Hits 4555 4555 - Misses 11072 11078 +6 Partials 270 270 ``` | [Files Changed](https://app.codecov.io/gh/emer/axon/pull/315?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=emer) | Coverage Δ | | |---|---|---| | [axon/hip\_net.go](https://app.codecov.io/gh/emer/axon/pull/315?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=emer#diff-YXhvbi9oaXBfbmV0Lmdv) | `0.00% <0.00%> (ø)` | |

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