Typos in Ple4Win Manual v4.7.1 and on website

[B Bharatadjaya MSc]

Hey Shaswin, thanks for your feedback.
The following issues are fixed:
* Issue 1: "Analyses" is the plural form of "Analysis", hence the use of it in the above sentence is correct.
* Issue 2: "USA" is added to the list of countries that used Ple4Win.
* Issue 3: "NEN 3650-1+C1:2020" has been changed to "NEN 3650-1:2020".
* Issue 4: "NEN 3650-1+C1:2020" has been changed to "NEN 3650-1:2020" and the missing images have been added.
* Issue 5: "feed-back" is changed into "feedback" on the online Ple4Win help manual.
* Issue 6: "feed-back" is changed into "feedback" on the Ple4Win website.
* Issue 7: all "Steel in Steel" references have been changed to "Steel-in-Steel" on the Ple4Win website and the online manual.