fix on reading multiple route in Gaussian input file

[Ameyanagi]

Summary

This fixes the issue that the Gaussian input file fails to read multiple lines.

• When the route input has multiple lines as below, GaussianInput.from_string() fails around the parsing of the route. This was due to inappropriate line counting when the route is separated in multiple lines.
• few lines of code were added to parse the route and route_index.
• test files for routes with multiple lines.

Example of Gaussian input (header only) with multiple lines of the route that failed.

%nprocshared=28
%mem=60GB
%chk=test.chk
# opt freq wb97xd/gen nosymm scf=(qc,maxcycle=1024) geom=connectivity
pseudo=read

Todo (if any)

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[janosh]

Thanks! 👍

[Ameyanagi]

Thanks for merging!