Throw informative error for Windows style EOL (mainly for atom users)

[lorenzwalthert]

Ask people to use Unix style EOLs. Fixes #396.

[codecov-io]

Codecov Report

Merging #400 into master will increase coverage by 0.08%.
The diff coverage is 96.29%.

@@            Coverage Diff             @@
##           master     #400      +/-   ##
==========================================
+ Coverage   89.97%   90.06%   +0.08%     
==========================================
  Files          30       30              
  Lines        1437     1459      +22     
==========================================
+ Hits         1293     1314      +21     
- Misses        144      145       +1

Impacted Files	Coverage Δ
R/transform-files.R	100% <100%> (ø)	⬆️
R/utils.R	86.95% <100%> (ø)	⬆️
R/parse.R	82.79% <95.83%> (+3.92%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9b995fa...e92b1b8. Read the comment docs.