Add @cond command

[nystrom]

Add a @cond command to register an expression at the current infiltration point. The next time that point is hit, infiltration will occur only if the expression evaluates to true. This is less efficient than the @infiltrate cond macro, but is more flexible in that the condition can be updated dynamically.

Example:

julia> function f(x)
         out = []
         for i in x
           push!(out, 2i)
           @infiltrate
         end
         out
       end
f (generic function with 1 method)

julia> f([1,2,3,4,5,6,7,8,9,10])
Infiltrating f(x::Vector{Int64})
  at REPL[10]:5

infil> @cond i > 5

infil> @continue
Conditionally enabled infiltration at this infiltration point.

Infiltrating f(x::Vector{Int64})
  at REPL[10]:5

infil> i
6

I'll add some tests if this seems worthwhile to eventually merge.

[codecov-commenter]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (bdf8448) 75.39% compared to head (9b3b413) 75.53%.
Report is 5 commits behind head on master.

Files	Patch %	Lines
src/Infiltrator.jl	78.04%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #105      +/-   ##
==========================================
+ Coverage   75.39%   75.53%   +0.14%     
==========================================
  Files           1        1              
  Lines         382      421      +39     
==========================================
+ Hits          288      318      +30     
- Misses         94      103       +9     

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[pfitzseb]

Thanks for this (and sorry for the delay in reviewing this)! I added a test for this, so no need to worry about that from your end :)

[nystrom]

Oh, thanks a lot for accepting the PR!

[pfitzseb]

Btw, I also added a note in the docs that this only takes local variables into account. Not sure how prohibitive the overhead of doing the eval at infiltration time would be, but that would solve the "issue".

[theogf]

That's a really cool feature! Thanks for adding it!