Free resolutions updates

[ederc]

1. Adds an attribute algorithm to the underlying ChainComplex in order to correctly extend a partially computed free resolution.
2. Introduces algorithm options mres and nres for extension code.
3. Removes error message if free resolution is already complete and returns zero module instead.
4. Fixes return of zero module if index is higher than the length of the free resolution.

[afkafkafk13]

Please adjust doctest output.

[codecov]

Codecov Report

Merging #2836 (3cf0e3a) into master (35bf9a4) will increase coverage by 0.28%.
Report is 2 commits behind head on master.
The diff coverage is 72.22%.

@@            Coverage Diff             @@
##           master    #2836      +/-   ##
==========================================
+ Coverage   80.61%   80.89%   +0.28%     
==========================================
  Files         456      456              
  Lines       64663    66457    +1794     
==========================================
+ Hits        52125    53758    +1633     
- Misses      12538    12699     +161     

Files Changed	Coverage
src/Modules/UngradedModules.jl	72.22%