Stix-validator

Bug Fixes
- [36] Fixed "IDREF With Content" best practice checking code which flagged `Related_Objects` that had a child `Relationship` element incorrectly.
- [46] Fixed issue where parsing non-STIX Profile xlsx files raised an uncaught exception.
- [47] Fixed `--recursive` behavior on `stix_validator.py`
- [48] Changed generated schematron to wrap each `<rule>` in a `<pattern>` element thereby resolving the issue where overlapping rule contexts resulted in `<assert>` and `<report>` directives not firing.

This is a bug fix release.

Bug Fixes
- [45] Fixed issue where error format strings relied on the presence of a non-existent `InstanceMapping` instance attribute.

Major Changes
- Installable API `pip install stix-validator`
- Bundled STIX v1.0 - v1.1.1 schemas
- Added unit tests
- Documentation (API/scripts/installation/getting started) added to http://stix-validator.readthedocs.org
- Changed versioning scheme to [semantic versioning](http://www.semver.org)

Resolved Issues
- [3] Added best practice check for `condition` presence in `Observable` instances under STIX Indicators.
- [4] Added best practice check for marking controlled structure XPath tests
- [9] Added best practice check for timestamp usage.
- [10] Added best practice check that verifies STIX component versions are up to date for a given STIX version.
- [11] Added best practice check for latest controlled vocabulary use
- [29] Added `--schema-dir` flag for validation against non-bundled schemas
- [34] `stix_validator.py` exit status codes are nonzero if validation fails or error occurs.
- [35] Added `--recursive` flag to `stix_validator.py` for descending into input directories.

- Cleanup and refactor of `sdv.py`
- Made it easier to call `sdv.py` from another process by making `settings.py` aware of its filesystem location
- Made input files/dir a positional argument and removed `--input-file` and `--input-dir` arguments (see README)
- Added more format checks that raise Exceptions if profile is malformed.
- Fixed 31 which prevented profile conversion/translation from being possible
- JSON results are keyed off of filename now (better for when multiple files are validated)

- Support for validating against all versions of STIX
- Added `settings.py` file that maps STIX versions to STIX schema directories
- PEP8 cleanup
- Updated examples in the `examples/` directory
- Redesign of validator code and package/module layout
- Added support for `tox` and Travis CI (thanks mblayman!)