Configuration of fontconfig to use heavier weights of Iosevka font.

fonts.conf

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
  <!-- Use heavier weights -->
  <match target="pattern">
    <test name="family"><string>Iosevka</string></test>
    <test name="weight" compare="eq"><const>regular</const></test>
    <edit name="weight" mode="assign" binding="strong"><const>semibold</const></edit>
  </match>
  <match target="pattern">
    <test name="family"><string>Iosevka</string></test>
    <test name="weight" compare="eq"><const>bold</const></test>
    <edit name="weight" mode="assign" binding="strong"><const>heavy</const></edit>
  </match>
</fontconfig>