Bump resolver to lts-19.7

Update discussion of **text**'s UTF-16 problem, closes #119.

core-text/lib/Core/Text/Rope.hs

@@ -39,11 +39,13 @@ sequence requires.
 
 The second way is through the opaque @Text@ type of "Data.Text" from the
 __text__ package, which is well tuned and high-performing but suffers from the
-same design; it is likewise backed by arrays. Rather surprisingly, the storage
-backing Text objects are encoded in UTF-16, meaning every time you want to
+same design; it is likewise backed by arrays. (Historically, the storage
+backing Text objects was encoded in UTF-16, meaning every time you wanted to
 work with unicode characters that came in from /anywhere/ else and which
-inevitably are UTF-8 encoded you have to convert to UTF-16 and copy into a new
-array, wasting time and memory.
+inevitably were UTF-8 encoded they had to be converted to UTF-16 and copied
+into a further new array! Fortunately Haskell has recently adopted a UTF-8
+backed @Text@ type, reducing this overhead. The challenge of appending pinned
+allocations remains, however.)
 
 In this package we introduce 'Rope', a text type backed by the 2-3
 'Data.FingerTree.FingerTree' data structure from the __fingertree__ package.

stack.yaml

@@ -1,4 +1,4 @@
-resolver: lts-18.28
+resolver: lts-19.7
 packages:
  - ./core-data
  - ./core-text
@@ -7,9 +7,4 @@ packages:
  - ./core-webserver-servant
  - ./core-webserver-warp
  - .
-extra-deps:
- - hashable-1.3.5.0
- - semialign-1.2
- - servant-0.19
- - servant-server-0.19.1
- - time-compat-1.9.6.1
+extra-deps: []