intmodule exporting (#3148)

* IntModule

* intmodule works

* a bit of documentation

* formatting

* example and better test.  Rename all the things, now they are Blue!

* formatting

* typo

* move file

* indexes

* Update core/src/main/scala/chisel3/internal/firrtl/IR.scala

Co-authored-by: Schuyler Eldridge <schuyler.eldridge@gmail.com>

* Update docs/src/explanations/intrinsics.md

Co-authored-by: Schuyler Eldridge <schuyler.eldridge@gmail.com>

* Update docs/src/explanations/intrinsics.md

Co-authored-by: Schuyler Eldridge <schuyler.eldridge@gmail.com>

* simplify tests

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Co-authored-by: Schuyler Eldridge <schuyler.eldridge@gmail.com>