Add object selection (textobjects) (#385)

* Add textobjects for word

* Add textobjects for surround characters

* Apply clippy lints

* Remove ThisWordPrevBound in favor of PrevWordEnd

It's the same as PrevWordEnd except for taking the current char
into account, so use a "flag" to capture that usecase

* Add tests for PrevWordEnd movement

* Remove ThisWord* movements

They did not preserve anchor positions and were only used
for textobject boundary search anyway so replace them with
simple position finding functions

* Rewrite tests of word textobject

* Add tests for surround textobject

* Add textobject docs

* Refactor textobject word position functions

* Apply clippy lints on textobject

* Fix overflow error with textobjects

1 files changed, 10 insertions, 0 deletions

diff --git a/helix-core/src/selection.rs b/helix-core/src/selection.rs
index d99e2aff..63b9b557 100644
--- a/helix-core/src/selection.rs
+++ b/helix-core/src/selection.rs
@@ -130,6 +130,16 @@ impl Range {
     }
 }
 
+impl From<(usize, usize)> for Range {
+    fn from(tuple: (usize, usize)) -> Self {
+        Self {
+            anchor: tuple.0,
+            head: tuple.1,
+            horiz: None,
+        }
+    }
+}
+
 /// A selection consists of one or more selection ranges.
 /// invariant: A selection can never be empty (always contains at least primary range).
 #[derive(Debug, Clone, PartialEq, Eq)]