feat(.collapse): Add collapse argument to epoxy and all downstream functions

[gadenbuie]

Closes #114

epoxy("{letters[1:3]}")
#> a
#> b
#> c
epoxy("{letters[1:3]}", .collapse = " | ")
#> a | b | c

epoxy_latex("<< letters[1:3] >>", .collapse = " \\middot ")
#> a \middot b \middot c

epoxy_html("{{ letters[1:3] }}", .collapse = "<br>")
#> a<br>b<br>c

But note that the html inline transformer already collapses vector expressions.

epoxy_html("{{ li letters[1:3] }}", .collapse = "<br>")
#> <li>a</li><li>b</li><li>c</li>

[codecov]

Codecov Report

Merging #115 (06a96e4) into main (d7fed0e) will increase coverage by 3.34%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #115      +/-   ##
==========================================
+ Coverage   92.61%   95.95%   +3.34%     
==========================================
  Files          11       11              
  Lines         934      939       +5     
==========================================
+ Hits          865      901      +36     
+ Misses         69       38      -31     

Files Changed	Coverage Δ
R/engines.R	94.15% <100.00%> (ø)
R/epoxy.R	94.56% <100.00%> (+0.31%)	⬆️

... and 1 file with indirect coverage changes

[github-actions]

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