Start to implement advanced search query language

docs/index.markdown

@@ -71,6 +71,7 @@ Using Kanboard
 
 ### More
 
+- [Search syntax](search.markdown)
 - [Command line interface](cli.markdown)
 - [Syntax guide](syntax-guide.markdown)
 - [Frequently asked questions](faq.markdown)

docs/search.markdown

@@ -0,0 +1,106 @@
+Advanced Search Syntax
+======================
+
+Kanboard use a simple query language for advanced search.
+
+Example of query
+----------------
+
+This example will returns all tasks assigned to me with a due date for tomorrow and that have a title that contains "my title":
+
+```
+assigne:me due:tomorrow my title
+```
+
+Search by assignee
+------------------
+
+Attribute: **assignee**
+
+Query with the full name:
+
+```
+assignee:"Frederic Guillot"
+```
+
+Query with the username:
+
+```
+assignee:fguillot
+```
+
+Multiple assignee lookup:
+
+```
+assignee:user1 assignee:"John Doe"
+```
+
+Kanboard will search tasks assigned to the "user1" or "John Doe".
+
+Query for unassigned tasks:
+
+```
+assignee:nobody
+```
+
+Query for my assigned tasks
+
+```
+assignee:me
+```
+
+Search by color
+---------------
+
+Attribute: **color**
+
+Query to search by color id:
+
+```
+color:blue
+```
+
+Query to search by color name:
+
+```
+color:"Deep Orange"
+```
+
+Search by due date
+------------------
+
+Attribute: **due**
+
+Query to search tasks due today:
+
+```
+due:today
+```
+
+Query to search tasks due tomorrow:
+
+```
+due:tomorrow
+```
+
+Query to search tasks due yesterday:
+
+```
+due:yesterday
+```
+
+Query to search tasks due with the exact date:
+
+```
+due:2015-06-29
+```
+
+The date must use the ISO8601 format: **YYYY-MM-DD**.
+
+Operators supported:
+
+- Greater than: **due:>2015-06-29**
+- Lower than: **due:<2015-06-29**
+- Greater than or equal: **due:>=2015-06-29**
+- Lower than or equal: **due:<=2015-06-29**
+