The forward declarations cause `Exception` to be inferred - also,
`llrecv` is an internal implementation detail and the type of the
received item is controlled by generics, thus the ValueError raised
there seems out of place for the generic api.
Raising exceptions halfway through a memory allocation is undefined
behavior since exceptions themselves require multiple allocations and
the allocator functions are not reentrant.
It is of course also expensive performance-wise to introduce lots of
exception-raising code everywhere since it breaks many optimisations and
bloats the code.
Finally, performing pointer arithmetic with signed integers is incorrect
for example on on a 32-bit systems that allows up to 3gb of address
space for applications (large address extensions) and unnecessary
elsewhere - broadly, stuff inside the memory allocator is generated by
the compiler or controlled by the standard library meaning that
applications should not be forced to pay this price.
If we wanted to check for overflow, the right way would be in the
initial allocation location where both the size and count of objects is
known.
The code is updated to use the same arithmetic operator style as for
refc with unchecked operations rather than disabling overflow checking
wholesale in the allocator module - there are reasons for both, but
going with the existing flow seems like an easier place to start.
Per manual, `panics:on` affects _only_ `Defect`:s - thus `sysFatal`
should not redirect any other exceptions.
Also, when `sysFatal` is used in `nimPanics` mode, it should use regular
exception handling pipeline to ensure exception hooks are called
consistently for all raised defects.
* Implement Markdown indented code blocks
Additional indentation of 4 spaces makes a block an "indented code block"
(monospaced text without syntax highlighting).
Also `::` RST syntax for code blocks is disabled.
So instead of
```rst
see::
Some code
```
the code block should be written as
```markdown
see:
Some code
```
* Migrate RST literal blocks :: to Markdown's ones
