Implemented the 'help' builtin, and support for :h <topic> in ex mode

:h is an alias for the 'help' builtin.

'help' takes a single argument and tries to find a suitable match among the files in '$SHED_HPATH'

if a match is found, this file is opened in your pager

calling the 'help' builtin using :h in ex mode will preserve your current pending line

Cargo.toml

@@ -35,6 +35,7 @@ rand = "0.10.0"
 regex = "1.11.1"
 scopeguard = "1.2.0"
 serde_json = "1.0.149"
+tempfile = "3.24.0"
 unicode-segmentation = "1.12.0"
 unicode-width = "0.2.0"
 vte = "0.15"