Test that lazy val doesn't rewrite module  definitions.
Merge pull request #104 from DarkDimius/lazy-vals-obj

Test that lazy val doesn't rewrite module  definitions.
Merge pull request #102 from dotty-staging/transform/erasure

Transform/erasure
Fix error in lazy-vals.

Wrong helper method was used.
Merge pull request #106 from DarkDimius/fixes-lazy-vals-typo

Fix build: Fix error in lazy-vals.
Documentation and a bit of cleanup.

Added documentation for non-trivial logic in Contexts, Phases and
TreeTransforms.
Removed redundant vars and casts