WIP: Add OutputController basic functionality

[mandli]

This PR adds a first go at a controller for output that could hide a lot of the tedium and state behind doing file IO in PyClaw.

Initially this came out of a discussion (clawpack/visclaw#144) on how to fix some weirdness in the VisClaw gettime function.

[coveralls]

Coverage increased (+0.01%) to 26.58% when pulling 3da9c57 on mandli:add-output-controller into 78019c0 on clawpack:master.

[ketch]

This looks reasonable, but I think before merging it we should have an example of how it is used. Can you submit a replacement to clawpack/visclaw#144 that uses this?

I have this feeling that just creating gettime() function -- for now at least -- might result in less overhead. We eventually need to discuss how this object will fit with the existing Solution and Controller, which currently share responsibility for IO.

[mandli]

Ah sorry, forgot to issue the PR for that, fixed now.

[mandli]

I am thinking that perhaps this should be called IOController instead to indicate that it does not just deal with output. Any ideas?

[mandli]

I am thinking that this is going to have some wide-ranging impacts and that perhaps we may want to move this to a CEP which we could write next week. In the mean time we can extract the essential content (again) and get the bux fix in there at least.

[mandli]

Proposed CEP8 related to this PR.