Allow assigning to semaphore limit.

[ioquatix]

async-pool would benefit from being able to resize and increase the maximum limit, but to do this, increasing (or decreasing) the limit on a semaphore should be a well defined operation. The semantics are:

• On increasing the limit, some tasks may be immediately resumed.
• On decreasing the limit, some tasks may execute until the count is < than the limit.

Types of Changes

• New feature.

Contribution

• I added tests for my changes.
• I tested my changes locally.
• I agree to the Developer's Certificate of Origin 1.1.