Rewrite explanation of doc-source-url option more clearly, and fix encoding to show euro-sign correctly.
Merge pull request #3875 from pocket7878/issue/8699

SI-3875 Fix euro-sign in doc-source-url description
Bump version for 2.12.x

For this step, we still depend on _2.11 libraries (partest, xml,
parser-combinators).

After we release the first milestone of 2.12, we will update
versions.property to bootstrap to 2.12 dependencies.
WIP: trying to apply the Literal-based singleton types commit by @paulp to the master.
Fix non-working things.
Update check file.
Problems with null.
Update the check file.
This is needed for the tests to pass.
Added a macro to materialize an inhabitant for the singleton type.
Added a test with the Ranged class mentioned by @non.
Add inhabitant to the bincompat whitelist.
Marked potentiall places in code where constant type folding and singleton type inlining might occur.
Inlining functions with singleton result type.
More involved example with Ranged.
Needed for the tests to pass after adding the SingleInhabitant
Fix some parser problems, do deconst before inlining the ConstantType.
Make .type optional for literals.
A small cleanup of the code.