Fix dsn.path where Sentry runs at a non-root URL

with a DSN like https://A:B@host.example.com/sentry/123 ,
parseDSN() produces:

{ protocol: 'https',
  public_key: 'A',
  private_key: 'B',
  host: 'host.example.com',
  path: 'sentry',
  project_id: 123,
  port: 443 }

which means when a request is sent, it goes to sentry/api/store/
instead of /sentry/api/store/.

The change fixes dsn.path to always have a leading (and trailing)
/ and changes the HTTP transport to not append an extra one.

Adds a specific transport test for non-root sentry, and modifies
existing tests with the new behaviour.
Update Express instructions
Use raw-stacktrace 1.0.0 to use the features given in #50
Update readme to help people with this issue
Merge pull request #52 from imownbey/bump_raw_stacktrace_version

Bump raw stacktrace version
0.5.3
Merge pull request #44 from rcoup/patch-1

Fix dsn.path where Sentry runs at a non-root URL
Use new type assertion syntax (should.js ~2.0.1)
Merge pull request #53 from kivikakk/fix-shifted-dep

Use new type assertion syntax (should.js ~2.0.1)
0.5.4
Merge pull request #45 from rcoup/patch-2

Update Express instructions
lol dates
lol words
Don't log an exception from Express on 500s
0.5.5
Make culprit actually useful
0.5.6
Switch to a modern DSN
Collect a complete module path
Read error from x-sentry-error instead of the body