Predefined themes and a color bash script

Fix: #44

extra/colors.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env python
+
+print("\033[0mno color\n")
+
+for name, flag in [('normal      : ', ''),
+                   ('bold        : ', '1;'),
+                   ('italics     : ', '3;'),
+                   ('bold italics: ', '3;1;')]:
+    print("\033[0m{}".format(name), end='')
+    for code in range(8):
+        print("\033[0m\033[{}3{}m {:03d} ".format(flag, code, code), end='')
+    print("")
+
+
+print("\033[0m")
+
+for code in range(256):
+    print("\033[33;5;0m\033[38;5;{}m {:03d} ".format(code, code), end='')
+
+    if code <= 16:
+        if (code + 1) % 8 == 0:
+            print("\033[0m")
+            if (code + 1) % 16 == 0:
+                print("\033[0m")
+    else:
+        if ((code + 1) - 16) % 6 == 0:
+            print("\033[0m")
+            if ((code + 1) - 16) % 36 == 0:
+                print("\033[0m")

extra/themes.md

@@ -0,0 +1,58 @@
+## Color Themes
+
+Here are some color themes for pubs. Copy-paste them in your configuration
+under the [theme] section (while deleting or commenting the current theme).
+
+Some of those theme require 256 colors. You can see which color correspond
+to which code by executing the `colors.sh` script in the `extra` folder in
+your terminal.  
+
+
+### Color titles
+
+For light and dark backgrounds.
+You can modify the title color to suit your taste. Current value is dark red.
+```
+# messages
+ok       = 'green'
+warning  = '166'
+error    = 'bred'
+
+# ui elements
+filepath = 'bold'
+citekey  = ''
+tag      = ''
+
+# bibliographic fields
+author    = 'bold'
+title     = '124'
+publisher = ''
+year      = ''
+volume    = ''
+pages     = ''
+```
+
+### Light grey
+
+For dark backgrounds.
+
+```
+[theme]
+# messages
+ok       = '240'
+warning  = '240'
+error    = 'b240'
+
+# ui elements
+filepath = 'bold'
+citekey  = 'b250'
+tag      = '240'
+
+# bibliographic fields
+author    = 'b240'
+title     = '245'
+publisher = 'i240'
+year      = '252'
+volume    = '240'
+pages     = '240'
+```

pubs/config/spec.py

@@ -39,7 +39,7 @@ color = boolean(default=True)
 
 # Here you can define the color theme used by pubs, if enabled in the
 # 'formating' section. Predefined theme are available at:
-# https://github.com/pubs/pubs/blob/master/theme.md
+# https://github.com/pubs/pubs/blob/master/extra/themes.md
 
 # Available colors are: 'black', 'red', 'green', 'yellow', 'blue', 'purple',
 # 'cyan', and 'grey'. Bold colors are available by prefixing 'b' in front of