Tab theme configurable (#317)

Text style for tabs can be configured within
`theme.toml` with the dotted keys `tab.active` and `tab.inactive`.

The default style is the same as the former hard-coded style.

`theme.toml` has been restructured and comments have been
added to give a short documentation on each style item.

The documentation (`theme.toml.md`) has been enhanced, and
the excerpt of `theme.toml` with additional comments has
been removed from there.

That way it should be easier for devs to keep docs and the default
`theme.toml` in sync, and easier for users when the detail comments
can be found in the configuration file itself.

The conversion from `AppStyle` to `tui::style::Style` is now provided as
a function of `AppStyle` and a `From`-implementation for `Style` to
avoid having the same factory code repeating all over.

1 files changed, 39 insertions, 71 deletions

diff --git a/docs/configuration/theme.toml.md b/docs/configuration/theme.toml.md
index 8af774a..e946be6 100644
--- a/docs/configuration/theme.toml.md
+++ b/docs/configuration/theme.toml.md
@@ -1,11 +1,14 @@
 # theme.toml
 
-This file is used to theme joshuto
+This file is used to theme Joshuto.
 
-## Style
+As of now, all theming items are "text style" items where one can define the
+background color and the foreground color, and enable some font attributes.
 
-Each style has the following fields:
 
+## Style options
+
+Each style allows the following fields:
 ```toml
 # background color
 bg = "light_blue"
@@ -15,81 +18,46 @@ bold = false
 underline = false
 invert = false
 ```
+Each field is optional. If omitted, it defaults to the terminal default.
+
 
 ## Color
 
-Joshuto supports 16 colors as well as hex colors via `rgb(r,g,b)`
+Joshuto supports 16 colors as well as hex colors via `rgb(r,g,b)`.
+The 16 default colors are:
+* `black`
+* `red`
+* `blue`
+* `green`
+* `yellow`
+* `magenta`
+* `cyan`
+* `white`
+* `gray`
+* `dark_gray`
+* `light_red`
+* `light_green`
+* `light_yellow`
+* `light_blue`
+* `light_magenta`
+* `light_cyan`
 
-```
-black
-red
-blue
-green
-yellow
-magenta
-cyan
-white
-gray
-dark_gray
-light_red
-light_green
-light_yellow
-light_blue
-light_magenta
-light_cyan
-_
-```
 
-## Theme
+## Configuration Items
 
-joshuto supports theming via system file types as well as extensions
+You can find a complete list of the available configuration items with their default
+values and short explanations as comment in 
+[`theme.toml`](https://github.com/kamiyaa/joshuto/blob/main/config/theme.toml).
 
-System file types include:
+In general, `theme.toml` allows to specify the style of a few UI "widgets",
+and the file entries in the file lists.
 
-```toml
-# for selected files
-[selection]
-fg = "light_yellow"
-bold = true
-
-# for executable files
-[executable]
-fg = "light_green"
-bold = true
-
-# default theme
-[regular]
-fg = "white"
-
-# for directories
-[directory]
-fg = "light_blue"
-bold = true
-
-# for symlinks
-[link]
-fg = "cyan"
-bold = true
-
-# for invalid symlinks
-[link_invalid]
-fg = "red"
-bold = true
-
-# for sockets
-[socket]
-fg = "light_magenta"
-bold = true
-```
+The file entries can be styled by their basic system file type and by their extension.
+The extension-specific style overrides the basic style.
 
-Via extensions
+Special file entries (as of now, executable files and invalid symlinks) have
+a specific style that overrides the former file-type-styles.
+
+Last but not least, there are styles for _selected_ files which override all the former
+styles.
 
-```toml
-[ext]
-[ext.jpg]
-fg = "yellow"
-[ext.jpeg]
-fg = "yellow"
-[ext.png]
-fg = "yellow"
-```