title: Qt #include not working with External Library
body: <p>I am fairly new to Qt 5 and Qt Creator . I created a library project called D20Controls. I have the D20Controls.lib file. In my project, I want to use classes of my lib D20Controls. So I right-click on my project and do Add Library... I choose External library and I browse up to my D20Controls.Lib file. Now everything seems to be added correctly to my .pro file. </p>
  
  <pre><code>win32:CONFIG(release, debug|release): LIBS += -L$$PWD/../../build-D20Controls-Desktop_Qt_5_1_1_MSVC2012_64bit-Debug/release/ -lD20Controls
  else:win32:CONFIG(debug, debug|release): LIBS += -L$$PWD/../../build-D20Controls-Desktop_Qt_5_1_1_MSVC2012_64bit-Debug/debug/ -lD20Controls
  
  INCLUDEPATH += $$PWD/../../build-D20Controls-Desktop_Qt_5_1_1_MSVC2012_64bit-Debug/debug
  DEPENDPATH += $$PWD/../../build-D20Controls-Desktop_Qt_5_1_1_MSVC2012_64bit-Debug/debug
  
  win32:CONFIG(release, debug|release): PRE_TARGETDEPS += $$PWD/../../build-D20Controls-Desktop_Qt_5_1_1_MSVC2012_64bit-Debug/release/D20Controls.lib
  else:win32:CONFIG(debug, debug|release): PRE_TARGETDEPS += $$PWD/../../build-D20Controls-Desktop_Qt_5_1_1_MSVC2012_64bit-Debug/debug/D20Controls.lib
  </code></pre>
  
  <p>but when I want to use it in my project 
  <code>#include &lt;D20Controls&gt;</code> or any .h file in it, I can't compile error like :
  ...main.cpp:4: error: C1083: Cannot open include file: 'D20Controls': No such file or directory</p>
  
  <p>How can I do use my lib ? (I have tried static linking and dynamic linking) </p>
  
  <p>What am I missing ?</p>