fixes some issues with underscores in float literals. add more tests.

fixes some potential issues with underscores in float literals.
adds more checks for badly positionned underscores in float literals.
adds more test files.

tests/float/tfloat6.nim

@@ -0,0 +1,21 @@
+discard """
+  file: "tfloat6.nim"
+  output: '''1e-06 : 1e-06
+1e-06 : 1e-06
+0.001 : 0.001
+1e-06 : 1e-06
+1e-06 : 1e-06
+10.000001 : 10.000001
+100.000001 : 100.000001'''
+"""
+
+import strutils
+
+echo "0.00_0001".parseFloat(), " : ", 1E-6
+echo "0.00__00_01".parseFloat(), " : ", 1E-6
+echo "0.0_01".parseFloat(), " : ", 0.001
+echo "0.00_000_1".parseFloat(), " : ", 1E-6
+echo "0.00000_1".parseFloat(), " : ", 1E-6
+
+echo "1_0.00_0001".parseFloat(), " : ", 10.000001
+echo "1__00.00_0001".parseFloat(), " : ", 1_00.000001

tests/float/tfloat7.nim

@@ -0,0 +1,26 @@
+discard """
+  file: "tfloat6.nim"
+  output: '''passed.
+passed.
+passed.
+passed.
+passed.
+passed.
+passed.'''
+"""
+
+import strutils
+template expect_fail(x: expr) =
+  try:
+    discard x
+    echo("expected to fail!")
+  except ValueError:
+    echo("passed.")
+
+expect_fail("1_0._00_0001".parseFloat())
+expect_fail("_1_0_00.0001".parseFloat())
+expect_fail("10.00.01".parseFloat())
+expect_fail("10.00E_01".parseFloat())
+expect_fail("10.00E_01".parseFloat())
+expect_fail("10.00E".parseFloat())
+expect_fail("10.00A".parseFloat())