add support for LF_CONFIG/DATA_HOME on unix

cc gokcehan#1209 gokcehan#1253

doc.go

@@ -288,16 +288,24 @@ History file should be located at:
 	Unix     ~/.local/share/lf/history
 	Windows  C:\Users\<user>\AppData\Local\lf\history
 
-You can configure the default values of following variables to change these locations:
+You can configure these locations with the following variables given with their order of precedences and their default values:
 
 	Unix
-	    $XDG_CONFIG_HOME  ~/.config
-	    $XDG_DATA_HOME    ~/.local/share
+	    $LF_CONFIG_HOME
+	    $XDG_CONFIG_HOME
+	    ~/.config
+
+	    $LF_DATA_HOME
+	    $XDG_DATA_HOME
+	    ~/.local/share
 
 	Windows
-	    %ProgramData%     C:\ProgramData
-	    %LOCALAPPDATA%    C:\Users\<user>\AppData\Local
-	    %LF_CONFIG_HOME%  If set, use this value instead of %LOCALAPPDATA%
+	    %ProgramData%
+	    C:\ProgramData
+
+	    %LF_CONFIG_HOME%
+	    %LOCALAPPDATA%
+	    C:\Users\<user>\AppData\Local
 
 A sample configuration file can be found at
 https://github.com/gokcehan/lf/blob/master/etc/lfrc.example

lf.1

@@ -334,19 +334,31 @@ History file should be located at:
     Windows  C:\eUsers\e<user>\eAppData\eLocal\elf\ehistory
 .EE
 .PP
-You can configure the default values of following variables to change these locations:
+You can configure these locations with the following variables given with their order of precedences and their default values:
 .PP
 .EX
     Unix
-        $XDG_CONFIG_HOME  ~/.config
-        $XDG_DATA_HOME    ~/.local/share
+        $LF_CONFIG_HOME
+        $XDG_CONFIG_HOME
+        ~/.config
+.EE
+.PP
+.EX
+        $LF_DATA_HOME
+        $XDG_DATA_HOME
+        ~/.local/share
 .EE
 .PP
 .EX
     Windows
-        %ProgramData%     C:\eProgramData
-        %LOCALAPPDATA%    C:\eUsers\e<user>\eAppData\eLocal
-        %LF_CONFIG_HOME%  If set, use this value instead of %LOCALAPPDATA%
+        %ProgramData%
+        C:\eProgramData
+.EE
+.PP
+.EX
+        %LF_CONFIG_HOME%
+        %LOCALAPPDATA%
+        C:\eUsers\e<user>\eAppData\eLocal
 .EE
 .PP
 A sample configuration file can be found at https://github.com/gokcehan/lf/blob/master/etc/lfrc.example

os.go

@@ -84,7 +84,10 @@ func init() {
 	}
 	gUser = u
 
-	config := os.Getenv("XDG_CONFIG_HOME")
+	config := os.Getenv("LF_CONFIG_HOME")
+	if config == "" {
+		config = os.Getenv("XDG_CONFIG_HOME")
+	}
 	if config == "" {
 		config = filepath.Join(gUser.HomeDir, ".config")
 	}
@@ -104,7 +107,10 @@ func init() {
 		filepath.Join(config, "lf", "icons"),
 	}
 
-	data := os.Getenv("XDG_DATA_HOME")
+	data := os.Getenv("LF_DATA_HOME")
+	if data == "" {
+		data = os.Getenv("XDG_DATA_HOME")
+	}
 	if data == "" {
 		data = filepath.Join(gUser.HomeDir, ".local", "share")
 	}