Mass replace '' -> None.

To make use of the new 'errors' argument.

'' was used in the original Perl tables both to mean an unknown replacement and
an intentional replacement with and empty string. Here I only replace it in
ranges I've added later where I'm reasonably sure that '' means unknown
replacement.

unidecode/x1d4.py

@@ -84,7 +84,7 @@
 'e',    # 0x52
 'f',    # 0x53
 'g',    # 0x54
-'',    # 0x55
+None,    # 0x55
 'i',    # 0x56
 'j',    # 0x57
 'k',    # 0x58
@@ -156,23 +156,23 @@
 'y',    # 0x9a
 'z',    # 0x9b
 'A',    # 0x9c
-'',    # 0x9d
+None,    # 0x9d
 'C',    # 0x9e
 'D',    # 0x9f
-'',    # 0xa0
-'',    # 0xa1
+None,    # 0xa0
+None,    # 0xa1
 'G',    # 0xa2
-'',    # 0xa3
-'',    # 0xa4
+None,    # 0xa3
+None,    # 0xa4
 'J',    # 0xa5
 'K',    # 0xa6
-'',    # 0xa7
-'',    # 0xa8
+None,    # 0xa7
+None,    # 0xa8
 'N',    # 0xa9
 'O',    # 0xaa
 'P',    # 0xab
 'Q',    # 0xac
-'',    # 0xad
+None,    # 0xad
 'S',    # 0xae
 'T',    # 0xaf
 'U',    # 0xb0
@@ -185,17 +185,17 @@
 'b',    # 0xb7
 'c',    # 0xb8
 'd',    # 0xb9
-'',    # 0xba
+None,    # 0xba
 'f',    # 0xbb
-'',    # 0xbc
+None,    # 0xbc
 'h',    # 0xbd
 'i',    # 0xbe
 'j',    # 0xbf
 'k',    # 0xc0
 'l',    # 0xc1
 'm',    # 0xc2
 'n',    # 0xc3
-'',    # 0xc4
+None,    # 0xc4
 'p',    # 0xc5
 'q',    # 0xc6
 'r',    # 0xc7

unidecode/x1d6.py

@@ -165,8 +165,8 @@
 'z',    # 0xa3
 'i',    # 0xa4
 'j',    # 0xa5
-'',    # 0xa6
-'',    # 0xa7
+None,    # 0xa6
+None,    # 0xa7
 'Alpha',    # 0xa8
 'Beta',    # 0xa9
 'Gamma',    # 0xaa
@@ -218,41 +218,41 @@
 'chi',    # 0xd8
 'psi',    # 0xd9
 'omega',    # 0xda
-'',    # 0xdb
-'',    # 0xdc
-'',    # 0xdd
-'',    # 0xde
-'',    # 0xdf
-'',    # 0xe0
-'',    # 0xe1
-'',    # 0xe2
-'',    # 0xe3
-'',    # 0xe4
-'',    # 0xe5
-'',    # 0xe6
-'',    # 0xe7
-'',    # 0xe8
-'',    # 0xe9
-'',    # 0xea
-'',    # 0xeb
-'',    # 0xec
-'',    # 0xed
-'',    # 0xee
-'',    # 0xef
-'',    # 0xf0
-'',    # 0xf1
-'',    # 0xf2
-'',    # 0xf3
-'',    # 0xf4
-'',    # 0xf5
-'',    # 0xf6
-'',    # 0xf7
-'',    # 0xf8
-'',    # 0xf9
-'',    # 0xfa
-'',    # 0xfb
-'',    # 0xfc
-'',    # 0xfd
-'',    # 0xfe
-'',    # 0xff
+None,    # 0xdb
+None,    # 0xdc
+None,    # 0xdd
+None,    # 0xde
+None,    # 0xdf
+None,    # 0xe0
+None,    # 0xe1
+None,    # 0xe2
+None,    # 0xe3
+None,    # 0xe4
+None,    # 0xe5
+None,    # 0xe6
+None,    # 0xe7
+None,    # 0xe8
+None,    # 0xe9
+None,    # 0xea
+None,    # 0xeb
+None,    # 0xec
+None,    # 0xed
+None,    # 0xee
+None,    # 0xef
+None,    # 0xf0
+None,    # 0xf1
+None,    # 0xf2
+None,    # 0xf3
+None,    # 0xf4
+None,    # 0xf5
+None,    # 0xf6
+None,    # 0xf7
+None,    # 0xf8
+None,    # 0xf9
+None,    # 0xfa
+None,    # 0xfb
+None,    # 0xfc
+None,    # 0xfd
+None,    # 0xfe
+None,    # 0xff
 )