shell: Fixes for windows

[jerry-skydio]

Switch to using a windows compatible "which"
function and properly catch the error if "man" is
not found.

Topic: win
Reviewers: brian-k
Fixes: 66

[jerry-skydio]

Reviews in this chain:
└#68 shell: Fixes for windows

[jerry-skydio]

#	head	base	diff	date	summary
0	34f3ceeb	aa41c582	diff	Oct 10 11:26 AM	2 files changed, 9 insertions(+), 3 deletions(-)
1	4d13407c	aa41c582	diff	Oct 10 11:30 AM	2 files changed, 7 insertions(+), 6 deletions(-)