Isofit

* Closes PR 55:
* Predicts high-resolution reflectance uncertainty based on the RSS of per-spectrum instrument noise and radiometric calibration uncertainty

* Closes PR 49:
* Adds global jit_enabled flag (defaults to False) to conditionally enable jit compilation.
* Adds global warnings_enabled flag
* Corrects the ISOFIT cli command so that it imports isofit.core.isofit and runs within a try-except, rather than defining it separately
*

* Tweaks to example code to remove calls to "run()".

Closes PR 53, addresses issues 48 and 50

NOTE: This release is not backwards compatible - imports have shifted with the code restructure. Please see examples.

* Includes the following updates from PR 46:
* Adds carbon & sulfate signature aerosol model.
* Modifies MODTRAN-relevant observer azimuth params.
* Enables different mixture choices per source
* Minor fixes

* Includes the following updates from PR 43:
* House cleaning of the import order so that local files are imported after
* Internalizing of package utilities into utils.py file/submodule.
* Merging of all tests to internal test submodule. All tests must pass for CI to pass.
* Addition of Isofit and Sunposition classes for non-CLI use, useful for example in creating cross-platform example scripts; the former has a run() method for separating out initialization. The nice thing is that these objects store the model inputs and outputs for subsequent analysis.
* Addition of cross-platform Python example scripts
* Removal of unused imports - more likely remain
* Removal of the utils and tests folder in the base directory
* Adds scikit-image requirement
* Updates docs with new install and release steps
* Removes autodeploy to Pypi from .travis.yml

Included with this release:

* PR 43 fixes import issues in the CLI scripts by moving programs to the bin directory. Utilities are still available separately in their respective directory for infrequent use.

Note for developers:

Update your PYTHONPATH to include the "isofit" base directory if you are running the code locally without installing the package.