Sum method in Numeric Stream

[garlontas]

💡 A sum method would be cool in Numeric Streams:

from pystreamapi import Stream

Stream.of([1, 2, 3, 4]).sum() # 10

Currently, this is only achievable with the reduce operation:

from pystreamapi import Stream

Stream.of([1, 2, 3, 4]).reduce(lambda x, y: x + y) # 10

sum should be only available in NumericStream because it could raise type errors.

[garlontas]

🚀 Pull request #37 adds the feature

[garlontas]

🎉 Feature implemented