:bug: Fix bug introduced in 9813c52

Fixes #25
Revert default `texPath` value to remove "pain"
Implement basic `latexmk` log parsing

Resolves the path to the output file generated as part of building the TeX
file. Takes into account the configured output directory preference.
Adjust `Builder` signature to match implementations
Fix bug due to accidental use of `path` module

The function `Builder::resolveLogFilePath` uses `path` module rather than
the `path` variable. Changes variable name to `childPath` and requires
the `path` module.

Closes #28
Implementing open-pdf support.

Presently the spec only tests for correct handling of errors. Do not really have idea what to test in case of success.
Increased time-out in the specs.