This change adds a `preparsed` subdirectory in the `encoding` directory,
with tests for which the result of the *encoding sniffing algorithm* at
https://html.spec.whatwg.org/#encoding-sniffing-algorithm is the
expected result — that is, tests for which the expected result is the
output of running *only* the encoding sniffing algorithm (of which the
main sub-algorithm is the so-called “meta prescan”) — without
also running the tokenization state machine and tree-construction stage.

This change also adds a README file that explicitly documents what the
expected results for the encoding tests are, based on whether or not
they’re in the `preparsed` subdirectory.

Without those changes, it’s unclear whether the expected results shown
in the existing tests are for the output of fully parsing the test data —
through the tokenization state machine and tree-construction stage — or
instead just the output of the encoding sniffing algorithm only. And
without those changes, we also don’t have any tests a system can use for
testing only the output from the encoding sniffing algorithm.

Fixes #28

This change adds a `preparsed` subdirectory in the `encoding` directory,
with tests for which the result of the *encoding sniffing algorithm* at
https://html.spec.whatwg.org/#encoding-sniffing-algorithm is the
expected result — that is, tests for which the expected result is the
output of running *only* the encoding sniffing algorithm (of which the
main sub-algorithm is the so-called “meta prescan”) — without
also running the tokenization state machine and tree-construction stage.

This change also adds a README file that explicitly documents what the
expected results for the encoding tests are, based on whether or not
they’re in the `preparsed` subdirectory.

Without those changes, it’s unclear whether the expected results shown
in the existing tests are for the output of fully parsing the test data —
through the tokenization state machine and tree-construction stage — or
instead just the output of the encoding sniffing algorithm only. And
without those changes, we also don’t have any tests a system can use for
testing only the output from the encoding sniffing algorithm.

Fixes #28