Division by zero as well as faulty memory operations may terminate the
Primus Machine. Previously we were just terminating it with a specific
exception. However, this exceptions should actually be represented by
an CPU/ABI-specific interrupt or trap. The proposed implementation
provides a mechanism that allows:

- trap the exception and translate it to a machine specific
  interrupt;

- ignore or fix it;

- catch it on a low-level.

The mechanism is based on the same idea as in the Linker that used the
primus_unresolved_handler to trap unresolved names. For each trap we
provide a corresponding observation, that could be used to install the
trap. The trap itself, is a special name, that could be linked (either
on a permanent basis, or from the observation). If the trap hanlder is
assigned, then it is invoked. Concrete behavior depends on a
particular trap, e.g.,

- for linker trap - the hanlder is invoked instead of the missing code;
- for the division by zero - if the handler returns
  then the result is undefined;
- for memory fault - the trap should fix the problem or terminate.

We also introduce the Pagefault exception, to represent memory
traps. We keep segfault as a non-maskable (non-preventable)
exception.

In addition, we have provided several new operations in the Linker
interface:
- unlink: for code unlinking, useful for removing traps
- lookup: useful for restoring other's traps

As a showcase, we also reimplemented some parts of the promiscuous
mode. Now we use the pagefault trap to prevent segmentation
faults. Also the fixing is more efficient as instead of mapping one
byte pages, we are mapping pages with size of up to 4k.

Besides others, this commit will also provide a fix for BinaryAnalysisPlatform#839.

handler
handler
handler
![handler](http://www.addletters.com/pictures/bart-simpson-generator/bart-simpson-generator.php?line=hanlder)