docs: clarify end_column value

I interpreted "the column where the token ends" to mean "a pointer
to the last character in the token", which would be the same as
the start column for a single-character token.

However, that's not what lark actually reports. Reword to clarify
this.

https://github.com/lark-parser/lark/issues/240

docs/classes.md

@@ -189,7 +189,7 @@ When using a lexer, the resulting tokens in the trees will be of the Token class
 * `line` - The line of the token in the text (starting with 1)
 * `column` - The column of the token in the text (starting with 1)
 * `end_line` - The line where the token ends
-* `end_column` - The column where the token ends
+* `end_column` - The next column after the end of the token. For example, if the token is a single character with a `column` value of 4, `end_column` will be 5.
 
 
 ## UnexpectedInput
@@ -216,4 +216,4 @@ Accepts the parse function (usually `lark_instance.parse`) and a dictionary of `
 
 The function will iterate the dictionary until it finds a matching error, and return the corresponding value.
 
-For an example usage, see: [examples/error_reporting_lalr.py](https://github.com/lark-parser/lark/blob/master/examples/error_reporting_lalr.py)
+For an example usage, see: [examples/error_reporting_lalr.py](https://github.com/lark-parser/lark/blob/master/examples/error_reporting_lalr.py)