Truncate semantic pointer names to 1 KB

[arvoelke]

Motivation and context:
Fixes #244. 1 KB was chosen somewhat arbitrarily, but it seems long enough to capture the majority of use cases where someone might want to read the name, while being a cheap amount of memory relative to the resource requirements of the semantic pointer itself and how it will be used.

I considered adding a warning, but it didn't seem important enough to let the user know (the fact that the name is being truncated seems inconsequential for most users)?

How has this been tested?
Added a unit test similar to the reproducing example from #244.

How long should this take to review?

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

Types of changes:

• Bug fix (non-breaking change which fixes an issue)

Checklist:

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

[jgosmann]

Thanks, LGTM.

Static checks are failing though because the commit message "body is too short". I think it is fine, but probably something that needs to be fixed on the nengo-bones side?

[hunse]

We may make that change in nengo-bones at some point. For now, though, I would recommend just changing the message to e.g. "This commit fixes #???" so that it's long enough.

[tbekolay]

We did decide to remove the commit body minimum length, but it'll take some time before that change is done as it's a ways down our priority list.

What I would do is copy in the context that is in the first post of this PR into the commit message. What's the harm in having additional context in the commit message body?

[arvoelke]

What I would do is copy in the context that is in the first post of this PR into the commit message.

Done.

[arvoelke]

3: B1 Line exceeds max length (285>72): "Fixes #244. 1 KB was chosen somewhat arbitrarily ...

Trying again.

[arvoelke]

/home/travis/build/nengo/nengo-spa/docs/license.rst.rst:31:broken link: http://www.numpy.org/license.html (404 Client Error: Not Found for url: https://numpy.org/license.html)

Trying again..

[arvoelke]

$ codespell -q 3 --skip=./build,*/_build,*-checkpoint.ipynb,./.eggs,./.git,*/_vendor --ignore-words-list=ba
./docs/user-guide/spa-intro.rst:129: contex ==> context
COMMAND 'codespell' FAILED```

Trying again...

[arvoelke]

It passed (unblocked)!

[arvoelke]

Note: will need to drop the last two commits after #252.