[otl] Update to version 4.0.451

[c72578]

The current version of otl is now also available with a filename including the version, e.g. otlv4_40451.zip [1, 2]

• Use variable OTL_VERSION in portfile
• Rename header file to otlv4.h
  This is the current default name of the header file and typically included using:
  #include "otlv4.h" or #include <otlv4.h>

[1] https://sourceforge.net/p/otl/discussion/208859/thread/fdb9d3bacc/#45bf
[2] https://otl.sourceforge.net/otl3_down.htm

Describe the pull request

• What does your PR fix? Fixes issue #
  Update otl to the current version 4.0.451
  Simplify portfile by using a variable for the version
• Which triplets are supported/not supported? Have you updated the CI baseline?
  All triplets are supported. CI-baseline: NA
• Does your PR follow the maintainer guide?
  Yes

[JackBoosY]

2020-01-04T12:18:04.9047756Z The following files are already installed in C:/vsts/_work/3/s/installed/x86-windows and are in conflict with stb:x86-windows
2020-01-04T12:18:04.9049652Z 
2020-01-04T12:18:04.9051732Z Installed by nanovg:x86-windows
2020-01-04T12:18:04.9053626Z     include/stb_image.h

Could you add stb:x86-windows=skip to VCPKG_PATH/scripts/ci.baseline.txt ?
Nope, I will open a PR to fix this issue.

Thanks.

[JackBoosY]

Could you please resolve theses conflicts?

Thanks,

[c72578]

OK, I have resolved the conflicts now.
Background info:
In the meantime, otl has been partly updated in master.
See: 9c86098 and PR: #9107
The following changes of this PR are already in master now and have been removed from the commit message here:

• Use variable OTL_VERSION in portfile
• Rename header file to otlv4.h