Add basic sandbox documentation
Revert "Add basic sandbox documentation"

This reverts commit 6bfb5a200c2202baa313903c95ced835316b23aa.

The sandbox feature is already documented (see #1430).
Additionally, the documentation added in this commit is misleading:
'runhaskell Setup.hs sandbox CMD' doesn't work.
Update bootstrap.sh.
Merge pull request #1459 from Blaisorblade/topic/testsuite-failures

Test suite: canonicalize binary path before execution
Add Travis scripts from https://github.com/errge/hflags

Import those scripts unchanged from errge/hflags; next commit will adapt
them to Cabal.

These scripts will use Ceh to setup Haskell on Travis machines.

The original have Apache License, but @errge explained that license is
not a concern because they are so simple.
Fix Travis scripts to work on both Cabal and cabal-install

* Run actions for both Cabal and cabal-install
* Install also dependencies for tests
* Ensure we exit on failure (with `set -e`).
  The shebang line is ignored, so use `set -e` or `set -ex` inside the
  script. Thanks to @errge for pointing this out.

  Fix from @errge (errge/hflags), see
  https://github.com/Blaisorblade/cabal/commit/53fc1e2180966d1cd050009b4113bb5bacd5294d#commitcomment-3990476
* Be more verbose (set -x)
* Enable testsuite correctly
Rename README to README.md
Add Travis build status image