Remove unnecessary argument in Transcode functions.

[jgosmann]

Motivation and context:
With the new syntax, SemanticPointer can track their vocabulary. This makes the vocab argument in Transcode functions unneccessary as it can be retrieved from the Semantic Pointer that is passed in.

Interactions with other PRs:
Cherry-picked the commit from my local docs branch as it touches actual code and should be reviewed separately. Thus the same commit might at some point appear in PR #68.

How has this been tested?
existing tests

How long should this take to review?

• Quick (less than 40 lines changed or changes are straightforward)

Types of changes:

• Breaking change (fix or feature that causes existing functionality to change)

Checklist:

• I have read the CONTRIBUTING.rst document.
• [n/a] I have updated the documentation accordingly.
• [n/a] I have included a changelog entry.
• [n/a] I have added tests to cover my changes.
• I have run the test suite locally and all tests passed.

[jgosmann]

AppVeyor build is failing due to some conda/openblas f*** up (once again). 😠 Merging.