Make possible to change < and > (the tags' delimiters) by two other chars

[eldipa]

Consider the following python example taken from the official documentation:

>>> fib                                                                                                                        
<function fib at 10042ed0>

If we want to execute this we need to remove the memory address as this is likely to change from one run to another.

Using <...> is the correct solution but, the expected string is already using < and > so we cannot distinguish a literal < from the begin of a tag.

We need some way to change the delimiters, something like:

>>> fib     # byexample: +tags=()                                                                                              
<function fib at (...)>

[eldipa]

In 8.1.0 it less likely to have a false positive so this feature has less value.