Changed most "backticks" (grave accents) into apostrophes.

Quotations that are embraced by tick marks now look better, in most fonts.

libsrc/Makefile

@@ -93,7 +93,7 @@ INSTALL = install
 
 define INSTALL_recipe
 
-$(if $(PREFIX),,$(error variable `PREFIX' must be set))
+$(if $(PREFIX),,$(error variable "PREFIX" must be set))
 $(INSTALL) -d $(DESTDIR)$(datadir)/$(dir)
 $(INSTALL) -m0644 ../$(dir)/*.* $(DESTDIR)$(datadir)/$(dir)
 

libsrc/lynx/lynx-snd.s

@@ -1062,7 +1062,7 @@ SndSetValues:
                 ldx #4-1
 set0:                ldy SndOffsets,x
                   lda SndChannel+2,y
-                  _IFNE                        ; flag == 0 => don`t set
+                  _IFNE                        ; flag == 0 => don't set
 
             bit #$80
                     _IFNE                       ;