In debugprint, don't print the profile headers more then once and only add it if the profile isn't empty.

The merge optimization when applied with the destroy handler can be very slow.
I have one case that got speed up from 190s to 12s by this PR:

Original:
SeqOptimizer  OPT_FAST_RUN  time 190.461s for 2161/548 nodes before/after optimization
   1.280s for fgraph.validate()
   132.634s for callback
   time      - (name, class, index) - validate time
   170.167204s - ('merge3', 'MergeOptimizer', 38) - 0.000s
     MergeOptimizer
       nb fail= 7728 merged=    0 constant=    0
       time replace=170.17 validate=0.00 callback=128.92
       callbacks_time
(<theano.gof.toolbox.PreserveNames object at 0x7f46b8864310>, 0.04287838935852051)
(<theano.gof.toolbox.ReplaceValidate object at 0x7f46b33f43d0>, 0.06792092323303223)
(<theano.tensor.opt.ShapeFeature object at 0x7f46b8864890>, 0.44670534133911133)
(<theano.gof.destroyhandler.DestroyHandler object at 0x7f46b4a44810>, 1.9552459716796875)
(<theano.gof.opt.MergeFeature object at 0x7f46b8864650>, 126.08237051963806)
   10.041219s - ('canonicalize', 'EquilibriumOptimizer', 4) - 0.051s

New one:

 SeqOptimizer  OPT_FAST_RUN  time 12.338s for 2161/548 nodes before/after optimization
   1.219s for fgraph.validate()
   3.536s for callback
   time      - (name, class, index) - validate time
   4.779337s - ('gpu_opt', 'SeqOptimizer', 12) - 0.012s
     SeqOptimizer      gpu_opt  time 4.779s for 633/504 nodes before/after optimization
       0.012s for fgraph.validate()
       0.817s for callback
       4.748835s - ('gpu_local_optimizations', 'EquilibriumOptimizer', 1) - 0.012s
...
   0.002217s - ('merge3', 'MergeOptimizer', 38) - 0.000s
     MergeOptimizer
       nb fail=    0 merged=    0 constant=    0
       time replace=0.00 validate=0.00 callback=0.00

Add requirement specific to rtd

Fix Sphinx markup in docs

Add Docker images to the installation docs

automatic gpu selection no longer works in CUDA-TK 7.0

Enables float16 gemm on gpuarray when the cuda version supports it

This reverts commit 1814576c.

Mixed2

- pycuda initialization was also affected by the bug from CUDA 7.0

- fixing an issue introduced with CUDA-TK 7.0, when automatic selection
  of free gpu by os / library no longer works. Library always selects '0',
  which leads to crash in case of 'exclusive mode'.
- this fix is inspired by Dan Povey's fix for Kaldi:
  https://github.com/kaldi-asr/kaldi/commit/6548565445167e00125848f91d7da5f3f949b2a2
- it does a loop over gpus until a free gpu is taken.

Optimize local_fill_sink

fix shape mismatch in GpuDnnPoolGrad

Implement GpuAdvancedSubtensor1 for gpuarray

elemwise opt

Scan inplace opt

 - it is caused by modification of theano.config.experimental.local_alloc_elemwise_assert in T_local_switch_sink

computer, add one line in the test case to try
to know what happened when it fails