Improves RDBMS installation and documentation

.travis.yml

 install:
   - cd tracim && python setup.py develop; cd -
   - echo coveralls >> install/requirements.txt; echo
+  - cat install/requirements.postgresql.txt >> install/requirements.txt; echo
+  - cat install/requirements.mysql.txt >> install/requirements.txt; echo
   - pip install -r install/requirements.txt; echo
 
 before_script:

README.md

 
 You'll need to install the following packages :
 
-    sudo apt install git realpath python3 python-virtualenv python3-dev python-pip build-essential libxml2-dev libxslt1-dev python-lxml zlib1g-dev
-
-To keep things simple for now, we'll use `SQLite3` as database engine:
-
-    sudo apt install sqlite3
-
-If you want to send email asynchronously:
-
-    sudo apt install redis-server
+    sudo apt install git realpath python3 python-virtualenv python3-dev python-pip build-essential libxml2-dev libxslt1-dev python-lxml zlib1g-dev redis-server
 
 ## Get the source ##
 

doc/database.md

 
 If you already use/know `PostgreSQL`, you can directly go to *Test the database access*.
 
+#### Driver ####
+
+Tracim uses the `psycopg` driver between the `SQLAlchemy` ORM and the `PostgreSQL` RDBMS. Run the following command to install the right version:
+
+    pip install -r install/requirements.postgresql.txt
+
 #### Allowing local connections on PostgreSQL ####
 
 Debian `PostgreSQL` stores connections authorization in `/etc/postgresql/9.1/main/pg_hba.conf`. Edit this file and check that connection from `127.0.0.1` are allowed using user/password. You should find the following line in the file:
 
 #### Driver ####
 
-Tracim uses the `PyMySQL` driver between the `SQLAlchemy` ORM and the `MySQL` RDBMS. The only requirement is a pip installable package:
+Tracim uses the `PyMySQL` driver between the `SQLAlchemy` ORM and the `MySQL` RDBMS. Run the following command to install the right version:
 
-    pip install PyMySQL
+    pip install -r install/requirements.mysql.txt
 
 #### Create database ####
 

install/requirements.mysql.txt

+PyMySQL==0.7.11

install/requirements.postgresql.txt

+psycopg2==2.5.4

install/requirements.txt

 nose==1.3.4
 pbr==0.10.0
 prettytable==0.7.2
-psycopg2==2.5.4
 py4j==0.10.1
 pyasn1==0.1.9
 pyparsing==2.0.3
 typing==3.5.3.0
 rq==0.7.1
 click==6.7
-PyMySQL==0.7.11