devlist.cpp needs <iomanip>
Change file locking in devlist.hpp

Use timed_lock() instead of several try_lock()'s with random waiting
intervals.
Running tests on Travis-CI
Omit two_stencils test for Boost versions with known problems
Omit part of user_defined_stencil test for broken Boost versions
typo
Omit status icon from Doxygen output

I could not find a way to preserve it there, and the previous variant
was boken.
Win32 build
Moved assign_expression from vex::vector to operations.hpp

This allows to assign expressions to terminals other than vex::vector;
e.g. vector slices or permutations.
Making vector_view writable
Adding tests for writable slices and permutations
Example of writing to a slice in README
Making tagged terminals writable
Uniform processing of lhs and rhs expressions in assign_expression()
Fixed a couple of compilation warnings

* Unused parameter in tests/tagged_terminal.cpp
* Signed/unsigned comparison in tests/vector_view.cpp
Fixed bug in vector_arithmetics/combined_expressions test
Reorganized kernel caches in spmat.hpp and stencil.hpp

Moved kernel caches from static class members into local static
variables. This allows Intel OpenCL SDK not to crash at program exit.
Fixed bug in tests/vector_view.cpp

Permutation object was initialized with full context instead of a single
queue.
Adding vex::precondition function (checks runtime conditions)
Enforcing single-device condition for relevant operations

FFT, SpMatCCSR, vector slices and permutations will throw
std::runtime_error if used with more than one compute device.