Add FORGIT_STASH_SHOW_PREVIEW_GIT_OPTS

This variable can be used to tune the rendering of the stash preview.

The following example allows listing the content of the stash before
opening it.

FORGIT_STASH_SHOW_PREVIEW_GIT_OPTS="--patch-with-stat --stat-count=10"

README.md

@@ -163,12 +163,20 @@ For linux users `FORGIT_COPY_CMD` should be set to make copy work. Example: `FOR
 Options can be set via environment variables. They have to be **exported** in
 order to be recognized by `forgit`.
 
-For instance, if you want to order branches in `gcb` by the last committed date you could:
+For instance:
+
+- if you want to order branches in `gcb` by the last committed date, you could:
 
 ```shell
 export FORGIT_CHECKOUT_BRANCH_BRANCH_GIT_OPTS='--sort=-committerdate'
 ```
 
+- if you want to see a preview of the stashed items in `gss` preview, you could:
+
+```shell
+export FORGIT_STASH_SHOW_PREVIEW_GIT_OPTS="--patch-with-stat --stat-count=10"
+```
+
 ## shell aliases
 
 You can change the default aliases by defining these variables below.
@@ -243,7 +251,7 @@ These are passed to the according `git` calls.
 | `gct`    | `FORGIT_CHECKOUT_TAG_GIT_OPTS`                                              |
 | `gco`    | `FORGIT_CHECKOUT_COMMIT_GIT_OPTS`                                           |
 | `grc`    | `FORGIT_REVERT_COMMIT_GIT_OPTS`                                             |
-| `gss`    | `FORGIT_STASH_SHOW_GIT_OPTS`                                                |
+| `gss`    | `FORGIT_STASH_SHOW_GIT_OPTS`, `FORGIT_STASH_SHOW_PREVIEW_GIT_OPTS`          |
 | `gsp`    | `FORGIT_STASH_PUSH_GIT_OPTS`                                                |
 | `gclean` | `FORGIT_CLEAN_GIT_OPTS`                                                     |
 | `grb`    | `FORGIT_REBASE_GIT_OPTS`                                                    |

bin/git-forgit

@@ -395,7 +395,9 @@ _forgit_reset_head() {
 _forgit_stash_show_preview() {
     local stash
     stash=$(echo "$1" | cut -d: -f1)
-    _forgit_git_stash_show "$stash" | _forgit_pager diff
+    _forgit_stash_show_preview_git_opts=()
+    _forgit_parse_array _forgit_stash_show_preview_git_opts "$FORGIT_STASH_SHOW_PREVIEW_GIT_OPTS"
+    _forgit_git_stash_show "${_forgit_stash_show_preview_git_opts[@]}" -- "$stash" | _forgit_pager diff
 }
 
 _forgit_git_stash_show() {