Feature request: Add colon-separated path list in search-path

[Neved4]

This feels a concise solution for setups that call search-path several times to other git submodules or repos. This would greatly allow repetition, concatenating paths like the PATH variable:

Currently

tectonic test.tex           \
    -Z search-path="$foo"   \
    -Z search-path="$bar"   \
    -Z search-path="$baz"   \
    -Z search-path="$qux"   \
    -Z search-path="$plugh" \
    -Z search-path="$thud"  \

After

tectonic test.tex -Z search-path "$foo:$bar:$baz:$qux:$plugh:$thud"