: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
:bug: Ensure output file path is always absolute
Improve specs and execute them using real `LatexmkBuilder`

* Once again running specs using a real `Builder` implementation to verify
  that everything works when running against `latexmk` and not just a
  Happy Path™ mock builder.
* Makes sure all specs are properly handling the async nature of `latex::build`.
* Also removes invokation status variables in favor of `callCount` checking
  on the spies.
Add test case that verifies log parsing end-to-end
Simplify specs further
:bug: Fix platform detection typo
Add initial appveyor.yml
Install pre-packaged TeX Live :heart: