Normalize exported and provided deps to ##ImmutableSortedSet##

Summary:
These are created and eventually stored as ##ImmutableSortedSet##
types, but the interfaces in between their creation and their
member references are generalized around the ##Set## type which
forces a copy in the ##DefaultJavaLibrary## constructor.  I'm
entirely sure if we want to standardize on ##ImmutableSortedSet##
as the main ##BuildRule## container, but it seems nice to make
this consistent and avoid the copy.

Test Plan: ant test
Pass client environment to ProjectBuildFileParser.

Summary:
Previously ProjectBuildFileParser would always use the
process environment whether or not buckd was used. This change ensures
that ProjectBuildFileParser always uses the client environment. This
change also invalidates the Parser build rule cache on environment
changes in case build rules depend on the environment.

Test Plan: buck test --all
Fixes for several typos and typesetting problems in the docs.

Summary:
I read through all the docs over the weekend, and noticed several small typos and typesetting problems. Here are some fixes.

Closes #123

Test Plan: careful inspection