Add memory_limit functions

[oschulz]

Example - limit Julia worker processes, but not main process, to 4 GiB of RAM:

@always_everywhere begin
    using Distributed
    myid() =! 1 && memory_limit!(4*1024^3)
end

[oschulz]

CC @theHenks

[codecov]

Codecov Report

Attention: Patch coverage is 78.94737% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 70.14%. Comparing base (b949759) to head (fde1e72).

Files	Patch %	Lines
src/memory.jl	78.94%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #14      +/-   ##
==========================================
+ Coverage   70.00%   70.14%   +0.13%     
==========================================
  Files          19       20       +1     
  Lines        1227     1246      +19     
==========================================
+ Hits          859      874      +15     
- Misses        368      372       +4     

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