Add 24bit color aka "direct color" aka "truecolor"

Also added several TERMs to Mode as supporting 256 colors.

This also adds 256 color TERMs to Mode::TERM_256 and used the mode
Regexps inside the support Regexp. This required swapping the require
order, because Support now depends on those Regexps from Mode.

I matched this up with my local laptop's terminfo DB (Ubuntu 20.04, with
ncurses 6.2.20200212, and a bunch of extra terminal packages installed).
I did make "ansi" support more conservative and added "^" to a few of
the other support cases (tput is still a fallback), but everything else
became more liberal.

To query terminfo, I ran the following bash script and several like it:

```bash
for term in $(toe -a | awk '{ print $1 }' | sort -u | xargs); do
    printf "%3d %s\n" "$(TERM="$term" tput colors)" "$term"
done | sort -n
```

lib/tty/color.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
-require_relative "color/support"
 require_relative "color/mode"
+require_relative "color/support"
 require_relative "color/version"
 
 module TTY

lib/tty/color/mode.rb

@@ -3,7 +3,12 @@
 module TTY
   module Color
     class Mode
-      TERM_256 = /iTerm(\s\d+){0,1}.app/x
+      TERM_24BIT = /[+-]direct/
+      TRUECOLORS = 2 ** 24 # 8 bits per RGB channel
+
+      TERM_256 = /^(alacritty|iTerm\s?\d*\.app|kitty|mintty|ms-terminal|
+                    nsterm|nsterm-build\d+|terminator|terminology(-[0-9.]+)?|
+                    termite|vscode)$/x
 
       TERM_64 = /^(hpterm-color|wy370|wy370-105k|wy370-EPC|wy370-nk|
                  wy370-rv|wy370-tek|wy370-vb|wy370-w|wy370-wvb)$/x
@@ -15,7 +20,7 @@ class Mode
                  d430c-unix-s|d430c-unix-sr|d430c-unix-w|d470|d470-7b|d470-dg|
                  d470c|d470c-7b|d470c-dg|dg+color|dg\+fixed|dgunix\+fixed|
                  dgmode\+color|hp\+color|ncr260wy325pp|ncr260wy325wpp|
-                 ncr260wy350pp|ncr260wy350wpp|nsterm|nsterm-c|nsterm-c-acs|
+                 ncr260wy350pp|ncr260wy350wpp|nsterm-c|nsterm-c-acs|
                  nsterm-c-s|nsterm-c-s-7|nsterm-c-s-acs|nsterm\+c|
                  nsterm-7-c|nsterm-bce)$/x
 
@@ -30,7 +35,7 @@ def initialize(env)
       # Detect supported colors
       #
       # @return [Integer]
-      #   out of 0, 8, 16, 52, 64, 256
+      #   out of 0, 8, 16, 52, 66, 256, 2^24
       #
       # @api public
       def mode
@@ -51,6 +56,7 @@ def mode
       # @api private
       def from_term
         case @env["TERM"]
+        when TERM_24BIT then TRUECOLORS
         when /[\-\+](\d+)color/ then $1.to_i
         when /[\-\+](\d+)bit/   then 2 ** $1.to_i
         when TERM_256 then 256

lib/tty/color/support.rb

@@ -6,6 +6,25 @@ class Support
       SOURCES = %w[from_term from_tput from_env from_curses].freeze
       ENV_VARS = %w[COLORTERM ANSICON].freeze
 
+      TERM_REGEX = /
+        color|  # explicitly claims color support in the name
+        direct| # explicitly claims "direct color" (24 bit) support
+
+        #{Mode::TERM_256}|
+        #{Mode::TERM_64}|
+        #{Mode::TERM_52}|
+        #{Mode::TERM_16}|
+        #{Mode::TERM_8}|
+
+        ^ansi(\.sys.*)?$|
+        ^cygwin|
+        ^linux|
+        ^putty|
+        ^rxvt|
+        ^screen|
+        ^tmux|
+        ^xterm /xi
+
       # Initialize a color support
       # @api public
       def initialize(env, verbose: false)
@@ -47,7 +66,7 @@ def disabled?
       def from_term
         case @env["TERM"]
         when "dumb" then false
-        when /^screen|^xterm|^vt100|color|ansi|cygwin|linux/i then true
+        when TERM_REGEX then true
         else NoValue
         end
       end

spec/unit/mode_spec.rb

@@ -27,7 +27,16 @@
 
   context "#from_term" do
     {
+      "xterm+direct" => 16_777_216,
+      "vscode-direct" => 16_777_216,
       "xterm-256color" => 256,
+      "alacritty" => 256,
+      "mintty" => 256,
+      "ms-terminal" => 256,
+      "nsterm" => 256,
+      "nsterm-build400" => 256,
+      "terminator" => 256,
+      "vscode" => 256,
       "iTerm.app" => 256,
       "iTerm 2.app" => 256,
       "amiga-8bit" => 256,

spec/unit/support_spec.rb

@@ -90,7 +90,7 @@
     end
   end
 
-  context "#form_term" do
+  context "#from_term" do
     it "fails to find color for dumb terminal" do
       support = described_class.new({"TERM" => "dumb"})
       expect(support.from_term).to eq(false)
@@ -99,6 +99,8 @@
     it "inspects term variable for color capabilities" do
       support = described_class.new({"TERM" => "xterm"})
       expect(support.from_term).to eq(true)
+      support = described_class.new({"TERM" => "tmux-256color"})
+      expect(support.from_term).to eq(true)
     end
 
     it "fails to find color capabilities from term variable " do