Probably going to connect the remaining bizarro signals (DCD/DTR/DSR/RI) to GPIO and figure out them later.

ESP-12F pins:
 7 GPIO13 UART0_CTS
16 GPIO15 UART0_RTS
21    RXD UART0_RXD
22    TXD UART0_TXD

DB-9 / |  ESP12  |  Signal  |  Direction    |  Description
200LX  |         |          |               |
-------+---------+----------+---------------+----------------------------
    1  |      ?  |    DCD   |  Modem -> PC  |  Data Carrier Detect
    2  |     22  |    RxD   |  Modem -> PC  |  Received Data (by DTE)
    3  |     21  |    TxD   |  PC -> Modem  |  Transmitted Data (by DTE)
    4  |      ?  |    DTR   |  PC -> Modem  |  Data Terminal Ready
    5  |     15  |    GND   |  Common       |  Signal Ground
    6  |      ?  |    DSR   |  Modem -> PC  |  Data Set Ready
    7  |     16  |    RTS   |  PC -> Modem  |  Request To Send
    8  |      7  |    CTS   |  Modem -> PC  |  Clear To Send
    9  |      ?  |    RI    |  Modem -> PC  |  Ring Indicator
   10  |         | prot.GND |  Common       |  Shield