Change http code from 200 to 500 when proxying error

Proxying request will throw exception but return 200 if the current
leader crashes, which may affect the judgement of user whether the job
is successful or not. Changing it to 500 to avoid this question.
Add http auth support to the PUT request
Update README.md

updating link & language
Update README.md
Merge pull request #320 from depay/master

Change http code from 200 to 500 when proxying error
Merge pull request #321 from flixster/p/stieg/http_auth_fix_script

Add http auth support to the PUT request
Return 500 only if proxying exception with code 2xx

If other logical exception happens, proxy should still return the
related status, e.g. deleting a non-existed job. Only proxying exception
with code 2xx may cause problem.
Add some useful environment variables to the Chronos task

This adds the following environment variables and their purpose

CHRONOS_RESOURCE_CPU  - The CPU resources allocated to this job
CHRONOS_RESOURCE_DISK - The disk resources allocated to this job
CHRONOS_RESOURCE_MEM  - Tme memory resources allocated to this job

The value in these is certain programs (like the JVM) can use these
values to optimize how they run (like setting the -xmx parameter).
Honestly Mesos should do this but I figure it doesn't hurt to put
it here and later have Mesos provide it too.

Conflicts:
	src/main/scala/com/airbnb/scheduler/mesos/MesosTaskBuilder.scala
Merge pull request #324 from depay/master

Return 500 only if proxying exception with code 2xx
Merge pull request #325 from flixster/resource_envs

Add some useful environment variables to the Chronos task