Files on the target at runtime

fileOpen returns a handle with methods on it; NSIS’s FileWrite-style instructions are all reached that way.

Usage fileOpen(path, mode) → handle, where mode is "r", "w" or "a"

NSIS	Installua
`FileOpen`	`fileOpen(path, mode)` → `handle`
`FileRead`	`handle:read([maxlen])` → `string`
`FileWrite`	`handle:write(text)`
`FileReadByte`	`handle:readByte()` → `int`
`FileWriteByte`	`handle:writeByte(value)`
`FileReadWord`	`handle:readWord()` → `int`
`FileWriteWord`	`handle:writeWord(value)`
`FileReadUTF16LE`	`handle:readUtf16Le([maxlen])` → `string`
`FileWriteUTF16LE`	`handle:writeUtf16Le(text[, { … }])`
`FileSeek`	`handle:seek(offset[, mode])` → `int`
`FileClose`	`handle:close()`

local f = fileOpen(INSTDIR .. "/install.log", "w")
f:write("installed\r\n")
f:close()