doc/tutorial/basic: Unified TOC, next/prev, titles

* Added missing `"Raw" Strings` link to TOC
* Made title on bottom.md match the title listed in TOC
* Unified interpolfield title on TOC and linked page
* Added missing TOC Cycles section and unified case of cycle
  page titles

Change-Id: Ibbbc4a8e40656de33b1117ad7f844c05ee04e167
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/3120
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/doc/tutorial/basics/Readme.md b/doc/tutorial/basics/Readme.md
index e133552..44f9f49 100644
--- a/doc/tutorial/basics/Readme.md
+++ b/doc/tutorial/basics/Readme.md
@@ -23,6 +23,7 @@
   - [Comments](comments.md)
   - [Number Literals](numberlit.md)
   - [String Literals](stringlit.md)
+  - ["Raw" Strings](stringraw.md)
   - [Bytes](bytes.md)
 - References and Visibility
   - [References and Scopes](scopes.md)
@@ -49,10 +50,13 @@
 - Expressions
   - [Operators](operators.md)
   - [Interpolation](interpolation.md)
-  - [Interpolation in Field Names](interpolfield.md)
+  - [Interpolation of Field Names](interpolfield.md)
   - [List Comprehensions](listcomp.md)
   - [Field Comprehensions](fieldcomp.md)
   - [Conditional Fields](conditional.md)
   - [Null or Error coalescing](coalesce.md)
+- Cycles
+  - [Reference Cycles](cycle.md)
+  - [Cycles in Fields](cycleref.md)
   <!-- - Conversions -->
   <!-- - Functions (simulating) -->
diff --git a/doc/tutorial/basics/bottom.md b/doc/tutorial/basics/bottom.md
index 4cdf814..b3f9b24 100644
--- a/doc/tutorial/basics/bottom.md
+++ b/doc/tutorial/basics/bottom.md
@@ -2,7 +2,7 @@
 
 _Types ~~and~~ are Values_
 
-# Bottom
+# Bottom / Error
 
 Specifying duplicate fields with conflicting values results in an error
 or bottom.
diff --git a/doc/tutorial/basics/cycle.md b/doc/tutorial/basics/cycle.md
index ed30a91..3855994 100644
--- a/doc/tutorial/basics/cycle.md
+++ b/doc/tutorial/basics/cycle.md
@@ -2,7 +2,7 @@
 
 _Cycles_
 
-# Reference cycles
+# Reference Cycles
 
 CUE can handle many types of cycles just fine.
 Because all values are final, a field with a concrete value of, say `200`,
diff --git a/doc/tutorial/basics/cycleref.md b/doc/tutorial/basics/cycleref.md
index d29e650..91f4f73 100644
--- a/doc/tutorial/basics/cycleref.md
+++ b/doc/tutorial/basics/cycleref.md
@@ -2,7 +2,7 @@
 
 _Cycles_
 
-# Cycles in fields
+# Cycles in Fields
 
 Also, we know that unifying a field with itself will result in the same value.
 Thus if we have a cycle between some fields, all we need to do is ignore