Review, comment, and reformat IPA.txt, including feedback comments.
Review, comment, and reformat IPA.txt, including feedback comments.

Formatting includes:

- removing line wraps (Emacs Cmd-Q), to make text easier to read
- provide useful indentation
- call out caveats and notes more explictly

Stylistically, I prefer the document talk in 3rd person instead of "we".  The
term "we" is unambiguous, and sometimes refers to different things.  I've passed
over the existing paragraphs and made them speak more about specific entities
that compose the analyzer and what they do (e.g., ExprEngine) instead of "we"
referring to the analyzer.

Further, I have substituted some vague concepts such as "state" or "program
state" and replaced them with their precise implementation counterparts (e.g.,
ProgramState).  This makes the document more technically precise throughout the
entire narrative, which would sometimes use vague terms and other times precise
terms.

I've placed several comments within the document, which can be seen with
***TMK/COMMENT***, which indicate places that need to be enhanced or clarified,
or called out as questions about intended bheavior.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@162338 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang