Add support for quoting directive names

Now only unquoted, literal names are recognized as directives, for
example:

'print' = abc
print $print

3 files changed, 12 insertions, 0 deletions

diff --git a/tests/directive/buildfile b/tests/directive/buildfile
new file mode 100644
index 0000000..0f83717
--- /dev/null
+++ b/tests/directive/buildfile
@@ -0,0 +1,8 @@
+"print"  = a
+'print' += b
+pr"int" += c
+print'' += d
+
+print $print
+
+./:
diff --git a/tests/directive/test.out b/tests/directive/test.out
new file mode 100644
index 0000000..8e13e46
--- /dev/null
+++ b/tests/directive/test.out
@@ -0,0 +1 @@
+a b c d
diff --git a/tests/directive/test.sh b/tests/directive/test.sh
new file mode 100755
index 0000000..b898b3c
--- /dev/null
+++ b/tests/directive/test.sh
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+valgrind -q b -q | diff -u test.out -