Add information about GSL as a mandatory dependency

[skip ci]

INSTALL-LINUX

@@ -1,8 +1,9 @@
 Update Note: to build GoldenCheetah v3.6 we are using the APT Package
-Manager to install dependencies, including Qt 5.14.2, on Travis CI Ubuntu
-Xenial build environment.
+Manager to install dependencies, including Qt 5.14.2 and GSL, on Travis-ci
+Ubuntu Xenial build environment.
 You can check the travis/linux folder for the complete and updated build scripts,
 the minimum Qt version known to work is 5.9 with Qt WebEngine and Qt Charts.
+GSL - GNU Scientific Library is a mandatory dependency starting with v3.6
 
 Ale Martinez - May, 2020
 

INSTALL-MAC

@@ -1,8 +1,9 @@
 Update Note: to build GoldenCheetah v3.6 we are using the Homebrew Package
-Manager to install dependencies, including Qt 5.14.2, on Travis CI macOS High
-Sierra build environment.
+Manager to install dependencies, including Qt 5.14.2 and GSL, on Travis-ci
+macOS High Sierra build environment.
 You can check the travis/osx folder for the complete and updated build scripts,
 the minimum Qt version known to work is 5.9 with Qt WebEngine and Qt Charts.
+GSL - GNU Scientific Library is a mandatory dependency starting with v3.6
 
 Ale Martinez - May, 2020
 

INSTALL-WIN32

@@ -1,8 +1,9 @@
 Update Note: to build GoldenCheetah v3.6 we are using Microsoft Visual C++ 2017,
-included in Microsoft Visual Studio 2019, with Qt 5.14.2 on AppVeyor continuous
-integration platform.
+included in Microsoft Visual Studio 2019, with pre-installed Qt 5.14.2 and GSL
+insalled with vcpkg, on AppVeyor continuous integration platform.
 You can check the appveyor.yml for the complete and updated build script,
 the minimum Qt version known to work is 5.9 with Qt WebEngine and Qt Charts.
+GSL - GNU Scientific Library is a mandatory dependency starting with v3.6
 
 Ale Martinez - May, 2020
                                  +++++++++++++++++++++++

src/gcconfig.pri.in

@@ -8,6 +8,17 @@
 #CONFIG += debug
 #CONFIG += release
 
+# uncomment below and configure the location of the GNU scientific library,
+# this is a mandatory dependency.
+#
+# Linux/Mac - use apt/homebrew to install and edit to your install location
+#GSL_INCLUDES = /usr/include
+#GSL_LIBS = -lgsl -lgslcblas -lm
+#
+# Windows - use vcpkg to install and edit to your install location
+#GSL_INCLUDES = c:\vcpkg\installed\x64-windows\include
+#GSL_LIBS = -LC:\vcpkg\installed\x64-windows\lib -lgsl -lgslcblas
+
 # Uncomment below if you want an R chart
 # You will need R installed along with the Rcpp and RInside
 # packages. There is an R script in the `util' directory that
@@ -33,17 +44,6 @@
 #PYTHONINCLUDES = -I/Library/Frameworks/Python.framework/Versions/3.6/include/python3.6m
 #PYTHONLIBS = -L/Library/Frameworks/Python.framework/Versions/3.6/lib -lpython3.6m
 
-# uncomment below and configure the location of
-# the GNU scientific library. 
-#
-# Linux/Mac
-#GSL_INCLUDES = /usr/include
-#GSL_LIBS = -lgsl -lgslcblas -lm
-#
-# Windows - use vcpkg to install gsl and edit to your install location
-#GSL_INCLUDES = c:\vcpkg\installed\x64-windows\include
-#GSL_LIBS = -LC:\vcpkg\installed\x64-windows\lib -lgsl -lgslcblas
-
 # put output into a separate dir
 # to keep main directory clear
 #DESTDIR = .

travis/linux/before_script.sh

@@ -8,14 +8,12 @@ cp src/gcconfig.pri.in src/gcconfig.pri
 if [ -n "$TRAVIS_TAG" ]; then echo DEFINES += GC_VERSION=VERSION_STRING >> src/gcconfig.pri; fi
 # make a release build
 sed -i "s|#\(CONFIG += release.*\)|\1 static|" src/gcconfig.pri
-# lrelease command
 sed -i "s|^#QMAKE_CXXFLAGS|QMAKE_CXXFLAGS|" src/gcconfig.pri
 # Enable -lz
 sed -i "s|^#LIBZ_LIBS|LIBZ_LIBS|" src/gcconfig.pri
 # ICAL
 sed -i "s|#\(ICAL_INSTALL =.*\)|\1 /usr|" src/gcconfig.pri
 # LIBUSB
-#sed -i "s|#\(LIBUSB_INSTALL =\).*|\1 /usr|" src/gcconfig.pri
 sed -i "s|#\(LIBUSB_INSTALL =\).*|\1 /usr/local|" src/gcconfig.pri
 sed -i "s|#\(LIBUSB_LIBS    =.*\)|\1 -lusb-1.0 -ldl -ludev|" src/gcconfig.pri
 sed -i "s|#\(LIBUSB_USE_V_1 = true.*\)|\1|" src/gcconfig.pri