Changing Embedding example to C file.

Added SERVER_SOFTWARE CGI variable

Update UserManual.md

SheBang wikipedia link is broken due to the end parenthesis. I tried escaping it with backslash and it seems to be working now.

Consume \n in mg_fgets when reading from membuf

(mg_fgets) Don't consume more than size bytes when line cannot fit into buffer.

gcc complains about _MSC_VER being an undefined macro.