Release 0.12.0

* PR #80 and #94: Support Tide framework by a feature and an example.
* PR #91: Update basic examples to edition 2018.
* Issue #68, PR #90: Don't eat whitespace after a for loop.
* Issue #66, PR #89: Fix parse error for nested braces in expressions.
* PR #84: Use std::ascii::escape_default.
* PR #87: Provide ToHtml::to_buffer()
* Forbid unsafe and undocumented code.
* The build is on https://travis-ci.com/kaj/ructe now.
* Internal cleanup.

Thanks to @Aunmag and @prabirshrestha for reported issues and
contributed code.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ructe"
-version = "0.11.5-PRE"
+version = "0.12.0"
 authors = ["Rasmus Kaj <kaj@kth.se>"]
 description = "Rust Compiled Templates, efficient type-safe web page templates."
 documentation = "https://docs.rs/ructe"