Support v2 fstab format

Auto detect and support both the v1 and v2 fstab formats
Support putting TWRP style flags in a separate /etc/twrp.flags file

twrp.flags format is the same as twrp.fstab (v1 with TWRP flags)

Support using a wildcard in a block device and find all partitions:
/usb-otg vfat /dev/block/sda*

Support using sysfs entries (voldmanaged) and read uevents and scan for
wildcard partitions from uevent data. (twvold?)

May not be complete for some of the newer flags found in fstabs in newer
build trees and there is a slim chance of a crash if the user removes a
removable device while TWRP is performing actions. May need to add some
kind of mutex to prevent the 2 threads from causing this crash. We need
to start somewhere though and this change is pretty innocuous when not
using a v2 fstab.

Change-Id: I617d97c7db332cbe671a9d2b8ad98b3d9c4f03cc
diff --git a/twrp-functions.hpp b/twrp-functions.hpp
index 66781bb..9c149ea 100644
--- a/twrp-functions.hpp
+++ b/twrp-functions.hpp
@@ -47,9 +47,9 @@
 class TWFunc
 {
 public:
-	static string Get_Root_Path(string Path);                                   // Trims any trailing folders or filenames from the path, also adds a leading / if not present
-	static string Get_Path(string Path);                                        // Trims everything after the last / in the string
-	static string Get_Filename(string Path);                                    // Trims the path off of a filename
+	static string Get_Root_Path(const string& Path);                            // Trims any trailing folders or filenames from the path, also adds a leading / if not present
+	static string Get_Path(const string& Path);                                 // Trims everything after the last / in the string
+	static string Get_Filename(const string& Path);                             // Trims the path off of a filename
 
 	static int Exec_Cmd(const string& cmd, string &result);                     //execute a command and return the result as a string by reference
 	static int Exec_Cmd(const string& cmd);                                     //execute a command
@@ -82,7 +82,7 @@
 	static int read_file(string fn, vector<string>& results); //read from file
 	static int read_file(string fn, string& results); //read from file
 	static int read_file(string fn, uint64_t& results); //read from file
-	static int write_file(string fn, string& line); //write from file
+	static int write_to_file(const string& fn, const string& line);             //write to file
 	static bool Install_SuperSU(void); // Installs su binary and apk and sets proper permissions
 	static bool Try_Decrypting_Backup(string Restore_Path, string Password); // true for success, false for failed to decrypt
 	static string System_Property_Get(string Prop_Name);                // Returns value of Prop_Name from reading /system/build.prop