Implement missing exercises

[NobbZ]

There are a couple of exercises missing.

For the hacktoberfest I open up issues for the following exercises:

name	issue	PR(s)
raindrops	#186	#229
pangram	#187	#223
sieve	#188	#201
isogram	#189	#217
bracket push	#190	#241
binary search tree	#191
list ops	#192	#297
sublist	#193	#350
custom set	#194	#222
simple linked list	#195
poker	#196	#295
two fer	#197	#200
complex numbers	#198	#221

If your favorite exercise is missing here, but on the list of missing exercises you can implement it as well.

[sjwarner-bp]

Two-fer has been completed as of #200 .

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[NobbZ]

Please pause on this until after v2 has been released.