Upstream changes:
Changes in inline version 0.3.15 (2018-05-18)
Correct requireNamespace() call thanks (Alexander Grueneberg in #5).
Small simplification to .travis.yml; also switch to https.
Use seq_along instead of seq(along=...) (Watal M. Iwasaki) in #6).
Update package manual page using references to DESCRIPTION file [CRAN request].
Minor packaging updates.