feat: add transformations

Fixes #9

README.md

@@ -3,11 +3,12 @@
 [![pipeline status](https://gitlab.com/openstapps/logger/badges/master/pipeline.svg)](https://gitlab.com/openstapps/logger/commits/master)
 [![coverage report](https://gitlab.com/openstapps/logger/badges/master/coverage.svg)](https://gitlab.com/openstapps/logger/commits/master)
 
-This is a simple logger for TypeScript projects with colors for console output.
+This is a simple logger for TypeScript projects with transformations for the log output.
 
 Logs are only printed if their log level is equal or higher than the defined log level.
 
 ## Log Levels
+
 Available log levels are:
 - 1 - INFO
 - 2 - LOG
@@ -25,15 +26,18 @@ If you want to use logger in production (`NODE_ENV=production`) and allow all tr
 `ALLOW_NO_TRANSPORT` to `true`.
 
 ## SMTP
+
 This class also provides a simple implementation of an SMTP transport which can be used as a
 `TransportWithVerification` for the logger. You can use this to transport errors of the logger or to transport mails
 of your own monitoring solution.
 
 ### Usage
+
 You can instatiate it with a config or it will check for a config in the environment variables. Environment variables
 can overwrite the actual config values.
 
 Environment variables are:
+
 * SMTP_AUTH_USER:      SMTP username
 * SMTP_AUTH_PASSWORD:  SMTP password
 * SMTP_HOST:           SMTP host
@@ -43,3 +47,15 @@ Environment variables are:
 * SMTP_SENDER_MAIL:    sender of the mail
 * SMTP_SENDER_NAME:    name of the sender
 * SMTP_SECURE:         `true` to enable tls
+
+## Transformations
+
+By default the logger will only add the log level to the message.
+
+You can change this behavior by setting other Transformers via `Logger.setTransformations`. If you do so, mind the order of the transformers.
+
+You may choose from the following:
+
+* `AddLogLevel`, which prepends the output with the log level
+* `Colorize`, which colorizes the output according to the log level
+* `Timestamp`, which prepends a timestamp to the output