feat: improve default user interface

Add a few fzf options to improve the default user interface. Users can
override the defaults using the FZF_DEFAULT_OPTS environment variable.
For example, to get the prompt back to the bottom of the screen:
    export FZF_DEFAULT_OPTS="--no-reverse"

See `man fzf` for more information about configuring the tool.

gh-fzf

@@ -108,12 +108,11 @@ fi
 # The following fzf options are shared by all commands. They are prepended to
 # the FZF_DEFAULT_OPTS environment variable so they can be overridden by users.
 export FZF_DEFAULT_OPTS='
---no-hscroll --no-exit-0 --header-lines=1
+--no-hscroll --no-exit-0 --header-lines=1 --cycle --reverse --delimiter="  "
 --preview-window="right,50%,wrap,~2,<60(down,40%,wrap)"
---delimiter="  "
 --preview-label="(alt+P: toggle preview) (alt+H: toggle hints)"
---bind="alt-P:toggle-preview"
---bind="alt-H:toggle-header"
+--bind="alt-P:toggle-preview" --bind="alt-H:toggle-header"
+--color "fg:#ebdbb2,fg+:#ebdbb2,bg:#282828,bg+:#3c3836,hl:#d3869b:bold,hl+:#d3869b,info:#83a598,prompt:#bdae93,spinner:#fabd2f,pointer:#83a598,marker:#fe8019,header:#928374,label:#83a598"
 --bind="ctrl-r:reload(eval \"$FZF_DEFAULT_COMMAND\")"
 --bind="alt-1:reload(eval \"$FZF_DEFAULT_COMMAND -L100\")"
 --bind="alt-2:reload(eval \"$FZF_DEFAULT_COMMAND -L200\")"
@@ -125,7 +124,7 @@ export FZF_DEFAULT_OPTS='
 --bind="alt-7:reload(eval \"$FZF_DEFAULT_COMMAND -L700\")"
 --bind="alt-8:reload(eval \"$FZF_DEFAULT_COMMAND -L800\")"
 --bind="alt-9:reload(eval \"$FZF_DEFAULT_COMMAND -L900\")"
-'" $FZF_DEFAULT_OPTS --no-select-1 --ansi --no-multi"
+'"$FZF_DEFAULT_OPTS"' --no-select-1 --ansi --no-multi'
 # Overriding the three options above breaks gh-fzf, so append them instead.
 
 # --------------------------------------------------------------------- }}}
@@ -466,7 +465,7 @@ $global_binds
 
 "
 
-    FZF_DEFAULT_COMMAND="GH_FORCE_TTY=$gh_columns gh release $release_template list -L $GH_FZF_DEFAULT_LIMIT $*" \
+    FZF_DEFAULT_COMMAND="GH_FORCE_TTY=$gh_columns gh release list $release_template -L $GH_FZF_DEFAULT_LIMIT $*" \
         fzf \
         --preview='GH_FORCE_TTY=$FZF_PREVIEW_COLUMNS gh release view {1} '"$repo_flag" \
         --header="$release_header" \