beautify code with clang-format

[stevengj]

Following up on #657, this PR makes no changes except to run clang-format -i on all of the C++ code, giving it a uniform formatting. (Previously, the code was a mishmash of styles due to different programmers and editor settings over the years, along with mangled indentation from tab/spaces conversions.)

Once this is merge, existing PR's and other branches will have zillions of conflicts, but if you follow a very careful procedure then this can be dealt with automatically:

1. First rebase onto the previous commit to this one (0545e3f) and fix any conflicts.

2. Then run clang-format -i on your code and commit it.

3. Then rebase onto this commit (b99fe3f), ignoring conflicts with git rebase -Xtheirs

Summary:

Instructions for rebasing other branches after this PR:

Replace MYBRANCH below with the name of your branch:

# update repo
git checkout master && git pull origin master # update master
rm -f python/*-python.cpp python/.deps/*-python.Plo # rm old swig files

# switch to your branch
git checkout MYBRANCH

# rebase onto PREVIOUS commit
git rebase 0545e3f1b82739c28c3bb3a9b383497520efe028

# reformat and rebase to THIS PR's commit
find . -name '*.*pp' | xargs clang-format -i
git commit -a -m "reformat"
git rebase -Xtheirs b99fe3fe5a709e5a9328cac04a29444e044fe21e

# finish rebase
git rebase master

[stevengj]

I tried the above procedure on #635 and it seems to have gone smoothly.

[zerothi]

Just a suggestion, when doing stuff like this, it might be useful to add the commit that only introduces formatting changes to a .git-blame-ignore-revs. In this way one can more easily backtrack stuff in terms of changes.

Some more context here: https://gist.github.com/kateinoigakukun/b0bc920e587851bfffa98b9e279175f2

(same goes for mpb if that PR goes in).