Scrollable tab-bar (#437)

This implements a scrollable tab bar, like discussed in #233.

This makes tabs easier to read, better utilizes the space in the top-bar
and makes handling many tabs way easier.

The display of the current directory has been removed.
The current tab will show the directory always in full form.
The directories of other tabs will be shown in full form if there is
enough space, otherwise, they will be shown in a short form.
If the available space in the top-bar is still not sufficient, scroll
tags will be added at each end.

The long-form is currently defined as the full, absolute path.
The short-form is currently defined as the last directory element of the
path.

The tab-bar is configurable in terms of font styling and style character
(like dividers, prefixes, and postfixes).

Documentation has been created in a separate file.

Collateral impact:
* The `tilde_in_titlebar` option for `[display]` in `joshuto.toml`
  has been removed.
  (Because the "current dir display" has been removed.)
* The `display_mode` option for `[tabs]` in `joshuto.toml`
  has been removed and with it, also the `tab_bar_mode` command.
  The appearance of index-numbers in tags is not configurable anymore.
  Numbers are shown if and only if there are more than one tab.
  This feature can be re-introduced later in some other form if still
  desired with the new tab-bar.
  With the new tab-bar, this configuration option did not make sense the
  way it was designed.
* The `max_len` option for `[tabs]` in `joshuto.toml`
  has been removed. (Because tabs don't have a fixed width anymore.)
* The function/feature of shortening paths by replacing heading path
  elements with their first character only has been removed.
  (Because I expect that this hard-to-interpret representation of a path
  will rarely be beneficial, now that there is a better space utilization in
  the top bar.)
* The "old" tab-bar configuration options have been removed.
* A `AppStyleOptionsRaw` struct has been introduced to allow handling of
  more complex default styling logic. Each styling attribute is defined
  there as an `Option` to indicate if a styling option has been
  set by the user or not.
* A `PathStyleIfSome` trait is now available in "utils" to patch ratatui
  styles with another, _optional_ style.

2 files changed, 23 insertions, 6 deletions

diff --git a/config/joshuto.toml b/config/joshuto.toml
index 9219ca0..455210d 100644
--- a/config/joshuto.toml
+++ b/config/joshuto.toml
@@ -18,7 +18,6 @@ scroll_offset = 6
 show_borders = true
 show_hidden = false
 show_icons = true
-tilde_in_titlebar = true
 # none, absolute, relative
 line_number_style = "none"
 
diff --git a/config/theme.toml b/config/theme.toml
index c26502f..fce3633 100644
--- a/config/theme.toml
+++ b/config/theme.toml
@@ -2,12 +2,30 @@
 ## Tabs
 ##########################################
 
-# Inactive tabs
-[tabs.inactive]
+[tabs]
+[tabs.styles]
 
-# Active tabs
-[tabs.active]
-invert=true
+# Style of active tab & current directory
+[tabs.styles.active]
+bg = "light_blue"
+fg = "black"
+bold = true
+
+# Style of inactive tabs
+[tabs.styles.inactive]
+
+# Style of the left/front tab scroll tag (when tabs overflow)
+[tabs.styles.scroll_front]
+fg = "yellow"
+bold = true
+
+# Style of the right/back tab scroll tag (when tabs overflow)
+[tabs.styles.scroll_back]
+fg = "yellow"
+bold = true
+
+# There are more style options and strings to configure
+# the tab-bar theme.
 
 ##########################################
 ## File List - Selections