Add support for shebang invocation - trim esh shebang from output

Resolves #17

Author: jirutka

esh

@@ -145,6 +145,9 @@ function end_text() {
 	state = "UNDEF"
 }
 function process_line() {
+	if (linenos[depth] == 0 && match(buff, "^#! */usr/bin/env esh([ \t]|$)")) {
+		return
+	}
 	print_nl = 1
 	linenos[depth]++
 

esh.1.adoc

@@ -119,6 +119,8 @@ Opening and closing tag may not be at the same line.
 Text outside a tag becomes literal text, but it is subject to any tagged shell code surrounding it.
 For example, text surrounded by a tagged *if* statement only appears in the output if the condition is true.
 
+If the first line of the template starts with `#!/usr/bin/env esh`, this line will be removed from the output (since 0.4.0).
+
 
 == EXAMPLES
 

tests/incl/esh-shebang.esh

@@ -0,0 +1,2 @@
+#! /usr/bin/env esh
+This line is included from incl/esh-shebang.esh

tests/test-esh-shebang.exp

@@ -0,0 +1 @@
+Hello from esh-shebang!

tests/test-esh-shebang.in

@@ -0,0 +1,2 @@
+#!/usr/bin/env esh
+Hello from <%= ${TEST_NAME#test-} %>!

tests/test-include-esh-shebang.exp

@@ -0,0 +1 @@
+This line is included from incl/esh-shebang.esh.

tests/test-include-esh-shebang.in

@@ -0,0 +1,2 @@
+#!/usr/bin/env esh
+<%+ incl/esh-shebang.esh %>.