Avoid calling get_uniform(max=1)

Calling get_uniform(max=1) results in a read_bits(n=0),
In get_uniform, the n param is renamed to max to clarify the
semantics. Asserts are added to detect calls to get_uniform()
and get_bits() that don't actually read anything.

Closes #76
7 jobs for master in 1 minute and 59 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Build
passed build-debian #4660
debian amd64

00:00:29

passed build-debian-aarch64 #4664
aarch64 debian

00:01:17

passed build-debian-aarch64-clang-5 #4665
aarch64 clang5 debian

00:00:53

passed build-debian-static #4661
debian amd64

00:00:29

passed build-macos #4666
macos

00:00:25

passed build-win32 #4662
win32

00:00:28

passed build-win64 #4663
win64

00:00:32