feat: stop hardcoding default instance and engine, also other minor changes.

git-svn-id: file:///srv/svn/repo/suwako/trunk@12 0b558ee1-521d-8b46-a41b-40029c97c055

README

@@ -4,14 +4,11 @@ Command-line client for SimplyTranslate in Go.
 
 Usage
 -----
--I string
-        Enter the text to be translated
--e string
-        Translation engine to use (default: google) (default "google")
--f string
-        Set the language to translate from. This can be skipped as it will autodetect the language you're translating from (default "auto")
--i string
-        Instance to use (default: https://simplytranslate.org/api/translate/) (default "https://simplytranslate.org/api/translate/")
--t string
-        Set the language to translate to (default: en) (default "en")
+-f [lang] (default: auto)
+-i [input]
+-t [lang] (default: en)
 
+Environment variables
+---------------------
+* STCLI_ENGINE
+* STCLI_INSTANCE