Use with for open
Remove default offset values

The offset is currently always provided anyway, but this avoids the
possibility of adding something to None.
Only ignore build directories in the root
Make proper link in README
Clarify LOAD_DATA comment
Make use of existing abstractions
Introduce deinterpret_int
Use heretical quotes to avoid escaping
Make to_bytes more consistent

When feeding join, using a list of strings is orders of magnitude faster
for longer strings than calling chain on them. Even though the latter
uses an iterator instead of a concrete list, it iterates over individual
characters.
Add decast_field

For consistency with interpret_atom's cast_field. Also throw in some
tuple unpacking.
Raise specific exception when parsing children
Go overboard with properties