Added description for new Stack Trace in all internal Exceptions and exceptions thrown with the Exception Object.

All exceptions thrown using the `Exception` object now include a Stack
Trace field. For example, this sample calls a label, which calls a
function, which throws an internal exception:
```
#include C:\Palabra\AutoHotkey\Lib
#include AhkLib.ahk

try {
Gosub RunMe
Return
} catch G_Exception {
CrashException("Uncaught Exception", G_Exception)
}

RunMe:
CDD("\BOGUS")
return

CDD(Folder) {
SetWorkingDir %Directory%
}
```
(In this example, CrashException is an AHK Function from my standard AHK
Library that just formats the exception nicely and displays it in a
debug dialog).

The actual caught exception thrown by SetWorkingDir looks like:
```
Message: 1
What   : SetWorkingDir
File   : C:\Temp\TestException.ahk
Line   : 16

File                      Line: Context Code
C:\Temp\TestException.ahk   17: CDD()   SetWorkingDir %Directory%
C:\Temp\TestException.ahk   12: RunMe:  CDD("\BOGUS")
C:\Temp\TestException.ahk    5: RunMe:  Gosub,RunMe
```

The first line is the line the exception happened on, or sometimes the
line before or after depending on how the exception happened.  The lines
below show the call stack back to the start of the program.  The first
two lines are self-explanatory.
• Context is the method or label active at the time.  For example, the
last 2 lines are both from the RunMe: label.  Labels end in : and
functions end in ()
• Code is the first 50 characters of the internal AHK version of the
code after parsing.  It usually matches the code without comments or
whitespace.  Multi-line statements are concatenated.

At the moment, this only works with internally thrown exceptions and
exceptions thrown using the `Exception` object, so your internal
exceptions should look like:
```
Throw Exception("This is Bogus", -1)
```
Instead of
```
Throw "This is bogus"
```
Improvements to ListLines and code for Exception Stack Trace