Fix RST documentation compilation errors introduced at various times in past

[robfrawley]

Q	A
Branch?	2.0
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	o
Tests pass?	yes
Fixed tickets
License	MIT
Doc PR

This PR fixes three compilation errors that were introduced into the RST documentation at various points in the past, including:

• Resources/doc/configuration.rst#L83: Bullet list ends without a blank line; unexpected unindent.
• Resources/doc/post-processors/png-quant.rst#L56: Unknown interpreted text role "string".
• Resources/doc/cache-resolver/aws_s3.rst#L121: Could not lex literal_block as "yaml".

As a result of the above fixed RST syntax issues, the documentation again compiled as expected without errors or warnings.

[coveralls]

Coverage remained the same at 72.871% when pulling f39242e on robfrawley:fix-documentation into 69966ef on liip:master.

[dbu]

thanks!
is the doc built in the ci so that we can directly notice errors when they are introduced?

[robfrawley]

thanks!
is the doc built in the ci so that we can directly notice errors when they are introduced?

@dbu: ATM, docs are not automatically built, but I am working a PR to introduce that so we can catch docs errors earlier in the future. Will follow up with additional PR once completed.