Add command to inc/dec number under cursor (#1027)

* Add command to inc/dec number under cursor

With the cursor over a number in normal mode, Ctrl + A will increment the
number and Ctrl + X will decrement the number. It works with binary, octal,
decimal, and hexidecimal numbers. Here are some examples.

0b01110100
0o1734
-24234
0x1F245

If the number isn't over a number it will try to find a number after the
cursor on the same line.

* Move several functions to helix-core

* Change to work based on word under selection

* It no longer finds the next number if the cursor isn't already over
  a number.
* It only matches numbers that are part of words with other characters
  like "foo123bar".
* It now works with multiple selections.

* Add some unit tests

* Fix for clippy

* Simplify some things

* Keep previous selection after incrementing

* Use short word instead of long word

This change requires us to manually handle minus sign.

* Don't pad decimal numbers if no leading zeros

* Handle numbers with `_` separators

* Refactor and add tests

* Move most of the code into core
* Add tests for the incremented output

* Use correct range

* Formatting

* Rename increment functions

* Make docs more specific

* This is easier to read

* This is clearer

* Type can be inferred

1 files changed, 2 insertions, 0 deletions

diff --git a/book/src/keymap.md b/book/src/keymap.md
index 7a896035..335e393b 100644
--- a/book/src/keymap.md
+++ b/book/src/keymap.md
@@ -72,6 +72,8 @@
 | `=`         | Format selection (**LSP**)                      | `format_selections`   |
 | `d`         | Delete selection                                | `delete_selection`    |
 | `c`         | Change selection (delete and enter insert mode) | `change_selection`    |
+| `Ctrl-a`    | Increment object (number) under cursor          | `increment`           |
+| `Ctrl-x`    | Decrement object (number) under cursor          | `decrement`           |
 
 #### Shell