Add Bulgarian translation. Closes #1706.

aegisub/packages/win_installer/fragment_translations.iss

@@ -39,6 +39,8 @@
 ; localization (commented out ones are out of date; some don't have wxstd.mo)
 Source: ..\..\po\ar.mo;          DestDir: {app}\locale\ar;    DestName: aegisub.mo; Flags: ignoreversion
 Source: src\mo\wxstd-ar.mo;      DestDir: {app}\locale\ar;    DestName: wxstd.mo;   Flags: ignoreversion
+Source: ..\..\po\bg.mo;          DestDir: {app}\locale\bg;    DestName: aegisub.mo; Flags: ignoreversion
+; Missing wxstd for Bulgarian
 Source: ..\..\po\ca.mo;          DestDir: {app}\locale\ca;    DestName: aegisub.mo; Flags: ignoreversion
 Source: src\mo\wxstd-ca.mo;      DestDir: {app}\locale\ca;    DestName: wxstd.mo;   Flags: ignoreversion
 Source: ..\..\po\cs.mo;          DestDir: {app}\locale\cs;    DestName: aegisub.mo; Flags: ignoreversion

aegisub/po/Makefile

@@ -4,6 +4,7 @@ include ../Makefile.inc
 
 PO = \
 	ar.po \
+	bg.po \
 	ca.po \
 	cs.po \
 	da.po \